©2011 Gilbert Ndjatou Page 207 Introduction to Classes  The concept of a class is the same as that of a structure: it is a user-defined data type that is used to create a group of variables that may have different data types.  In addition to the data members, a member of a class can also be a function.  A member function is in general specified in the class definition by its function prototype with its definition provided somewhere else in the program.  You define a class as follows: class { };  A member of a class (data or function) can be public or private.  In the definition of a class,  you use the label public to specify its public members and  the label private to specify its private members. Example C1 class Demo1 { public: double getValue2(void); // to return the value of the private data member void setValue2(double num); // to set the value of the private data member double getAverage( ); // to compute the average of both values double val1; // the public data member private: double computeSum( ); // to compute the sum of both values double val2; // the private data member }; ©2011 Gilbert Ndjatou Page 208 Definition of a Class Member Function  When you write the definition of a class member function, you must precede the name of the function in the function header by the name of that class followed by the scope resolution operator ( :: ).  A class data member (public or private) can be accessed in the body of a member function of that class.  A class member function (private or public) can be called in another member function of that class. Example C2 Definitions of the member functions of class Demo1: /*---------------------------------- function getValue2( ) --------------------------------------------------*/ /* returns the value of the private member variable */ double Demo1:: getValue2(void) { return (val2); } /*---------------------------------- function setValue2( ) --------------------------------------------------*/ /* set the value of the private member variable to the given value */ void Demo1:: setValue2(double num) { val2 = num; } /*---------------------------------- function getAverage( ) --------------------------------------------------*/ /* compute the average of both values and return it */ double Demo1:: getAverage(void) { double total; total = computeSum( ); return(total / 2); } /*---------------------------------- function computeSum( ) ------------------------------------------------*/ /* compute the sum of both values and return it */ double Demo1:: computeSum(void) { return (val1 + val2 ) ; } ©2011 Gilbert Ndjatou Page 209 Declaration of a Class Variable (or Object)  A class variable is called object.  You declare an object in the same way that you declare a structure variable.  As with structure variables, when you declare an object, a member variable is created for each data member of the class. Example C3 Declaration Effects in Memory Demo1 item1; item1.val1 item1.val2 Demo1 item2; item2.val1 item2.val2 Specifying the Members of an Object  You specify an object’s public member variable in the same way that you specify a member of a structure variable, by using the dot operator.  You call a class public member function on an object by preceding the function call with the name of that object, followed by the dot operator.  A private member variable of an object can only be specified in a member function or a friend function of the class of that object.  A private member function of a class can be called on an object only in a member function or a friend function of the class of that object.  A class member function can be called in a function that is not a class member function only on an object. Example C4 Given the class Demo1 of example C1 and object item1 defined in function main as follows: Demo1 item1; ©2011 Gilbert Ndjatou Page 210 We have the following access to the member functions and the member variable of object item1: Valid Access to the Members of Object item1 Effects 1. cin >> item1.val1; // read a value into the public member variable val1 2. item1.setValue2 (15); // set the private member variable val2 to 15 3. cout << endl << “The average of:\t” 4. << item1.val1 << “ and “ // output the value of the member variable val1 5. << item1.getValue2( ) << “ is: “ // output the value of the member variable val2 6. << item1.getAverage( ); // output the average of the values of both variables Invalid Access to the Members of Object item1 Reasons 1. cin >> item1.val2; // val2 is a private member variable 2. item1.computeSum( ); // computeSum is a private member function 3. getValue2( ); /* in a function that is not a class member function, a class member function must be called on an object */ Objects and the Assignment Operator  It is legal in C++ to assign an object to another object of the same class.  The assignment of an object to another generates the member-wise assignments of the member variables of both objects. Example C5 Given the class Demo1 of Example C1 and the following definitions of objects: Demo1 item1, item2; The assignment: item1 = item2; has the same effect as: item1.val1 = item2.val1; item1.setValue2( item2.getValue2( ) ); Notes 1. The concept of combining a number of items such as variables and functions into a package such as an object is called encapsulation. 2. In a class definition, you can have any number of occurrences of the labels public: and private: as shown in the following example: ©2011 Gilbert Ndjatou Page 211 class SampleClass { Public: void inputSomething( ); int stuff; private: int computeResult( int val); int val1; public: int setvalue( ); int val2; }; 3. In a class definition, the section between the opening brace { and the first access-specifier label, public: or private: is a private section. For example, the following two class definitions are identical: class SampleClass1 { int computeResult( int val); int val1; public: int setvalue( ); int val2; }; class SampleClass2 { private: int computeResult( int val); int val1; public: int setvalue( ); int val2; }; 4. It is a common practice to specify the public members of a class before the private members and to list the member function prototypes before the member variables as we have done with the definition of the class Demo1 of Example C1. ©2011 Gilbert Ndjatou Page 212 Exercise C1* Given the following class definition: class Automobile { public: void setPrice ( double newPrice ); // to set the value of price member variable void setProfit ( double newProfit ); // to set the value of profit member variable double getPrice ( ); // to return the value of price member variable private: double price; double profit; double getProfit ( ); // to return the value of profit member variable }; a. Write the definitions of the member functions setPrice, setProfit, getPrice, and getProfit. b. Given the following definitions of objects hyundai and jaguar in function main: Automobile hyunday, jaguar; Which of the following statements are invalid? Also provide the reasons why a statement is invalid. hyunday.price = 15000.00; jaguar.setPrice( 45000.00 ); cout << jaguar.getProfit ( ); jaguar.setProfit( ); cout << jaguar.getPrice ( ); jaguar = hyunday; setPrice ( 16500 ); c. Write a statement to set the profit member variable of object jaguar to 3500. d. Write a statement to read a price and set the price member variable of object hyunday to it. e. Write a statement to output the value of the price member variable of object jaguar. f. Is it possible to write a statement to output the value of the profit member variable of objet jaguar? Why? g. Write the statements to do the following: 1. Assign the value of each member variable of object jaguar to the corresponding member variable of object hyunday, and then, 2. Change the value of the member variable price of object hyunday to 24000.00. ©2011 Gilbert Ndjatou Page 213 Exercise C2 Given the following class Automobile defined in exercise C1: class Automobile { public: void setPrice ( double newPrice ); // to set the value of price member variable void setProfit ( double newProfit ); // to set the value of profit member variable double getPrice ( ); // to return the value of price member variable private: double price; double profit; double getProfit ( ); // to return the value of profit member variable }; a. And given the following definitions of objects sable and jeep in function main: Automobile sable, jeep; Which of the following statements are invalid? Also provide the reasons why a statement is invalid. cin >> jeep.profit; jeep.setPrice( 45000.00 ); cout << jeep.getProfit ( ); cout << jeep.getPrice ( ); sable.setProfit( ); jeep = sable; cout << getPrice( ); b. Write a statement to set the price member variable of object jeep to 22000.00. c. Write a statement to read a profit and set the profit member variable of object sable to it. d. Write a statement to output the value of the price member variable of object jeep. e. Write the statements to assign the value of each member variable of object jeep to the corresponding member variable of object sable, and then to change the value of member variable profit of object sable to 4000.00. Exercise C3 Write the definition of function main that does the following: a. Define an object of the class Demo1 (defined in example C1above) b. Read two values and set the two member variables of this object to those values. c. Output the values of the member variables of this object with appropriate messages. d. Compute and print the average value of the member variables of this object with an appropriate message. ©2011 Gilbert Ndjatou Page 214 Classes and Functions  A class can be the return type of a function: a function can return an object. Example C6 The following function reads the values for the two member variables of an object of the type class Demo1 (defined in example C1 above) and then returns that object. Demo1 inputValues (void) { Demo1 temp; double num; cin >> temp.val1; // read a value for the first member variable of the object /*--- read the second value and set the second member variable of the object to it--------*/ cin >> num; temp.setValue2(num); return (temp); } /*----------------------------------- the above function is called as follows ---------------------------*/ Demo1 item; item = inputValues( );  An object can be a value parameter of a function.  When a function with an object as value parameter is called, the value of each member variable of the object argument is copied to the corresponding member variable of the object parameter. Example C7 The following function receives an object of the class Demo1 (defined in example C1 above) as argument, and returns five times the average of the values of its member variables. double average5 (Demo1 item ) { double result; result = 5 * item.getAverage( ); return result; } ©2011 Gilbert Ndjatou Page 215 /*------------------------ the above function may be called as follows ---------------------------*/ Demo1 stuff; stuff.val1 = 10; stuff.setValue2 ( 12 ); cout << endl << average5( stuff ); After this call of function average5( ), its body is executed as if it was written as follows: double average5 (Demo1 item ) { item.val1 = stuff.val1; item.setValue2( stuff.getValue2( ) ); double result; result = 5 * item.getAverage( ); return result; }  An object can be a reference parameter of a function.  When a function with an object as a reference parameter is called, the object argument replaces the object parameter in the body of the function. Example C8 The following function receives an object of the class Demo1 (defined in example C1 above) as argument, and adds 3 to the value of each of its member variables. void add3 (Demo1 &item) { int num; item.val1 += 3; num = item.getValue2( ); item.setValue2( num + 3 ); } /*----------------------------------- the above function is called as follows ---------------------------*/ Demo1 someItem; someItem.val1 = 10; someItem.setValue2 ( 15 ); add3( someItem ); // someItem.value1 = 13 and someItem.value2 = 18 ©2011 Gilbert Ndjatou Page 216 After the above call of function add3( ), its body is executed as if it was written as follows: { int num; someItem.val1 += 3; num = someItem.getValue2( ); someItem.setValue2( num + 3 ); } Exercise C4* Using the definition of the class Demo1 given in example C1, do the following: a. Write a function addDemo1 that receives as arguments two objects of the class Demo1 and then builds and returns another object of the class Demo1 such that the value of each of its member variable of is the sum of the values of the corresponding member variables of the objects received as arguments. b. Write a code segment to do the following: i. Declare objects obj1 and obj2 of the class Demo1. ii. Set the values of the member variables of object obj1 to 5 and 7 respectively and those of the member variables of object obj2 to 10 and 15 respectively. iii. Create object objR of the class Demo1 such that the value of each of its member variables is the sum of the values of the corresponding member variables of the objects obj1 and obj2 by calling function addDemo1( ) defined in part a. Exercise C5* Using the definition of the class Demo1 given in example C1, do the following: a. Write a void function updateDemo1 that receives as argument an object of the class Demo1 and adds 10 to the value of its first member variable, and subtract 5 from the value of its second member variable. b. Write a code segment to do the following: Declare object obj of the class Demo1. Set the values of the member variables of object obj to 15 and 70 respectively.  Add 10 to the value of the first member variable of object obj and subtract 5 from the value of its second member variable by calling the function updaDemo1( ) defined in part a. ©2011 Gilbert Ndjatou Page 217 Exercise C6 The class Demo2 is defined as follows: class Demo2 { public: void setValues(double num1, double num2); // to set the values of both member variables double getValue1(void); // to return the value of member variable val1 double getValue2(void); // to return the value of member variable val2 double getAverage( ); // to compute the average of the values of both variables private: double val1; // the first data member double val2; // the second data member }; /*---------------------------------- function setValues( ) --------------------------------------------------*/ /* set the values of the member variables to the given values */ void Demo2:: setValues(double num1, double num2) { val1 = num1; val2 = num2; } /*---------------------------------- function getValue1( ) --------------------------------------------------*/ /* returns the value of the first member variable */ double Demo2:: getValue1(void) { return (val1); } /*---------------------------------- function getValue2( ) --------------------------------------------------*/ /* returns the value of the second member variable */ double Demo2:: getValue2(void) { return (val2); } /*---------------------------------- function getAverage( ) --------------------------------------------------*/ /* compute the average of both values and return it */ double Demo2:: getAverage(void) { return( (valu1 + valu2) / 2); } ©2011 Gilbert Ndjatou Page 218 Use the definition of the class Demo2 to do the following: 1. Declare object item of the class Demo2. 2. Read the values for the member variables of object item, and set the values of its member variables. 3. Compute the average of the values of the member variables of object item and print it. 4. Write a function named addDemo2( ) that receives as arguments two objects of the class Demo2 and then builds and returns another object of the class Demo2 such that the value of each of its member variables is the sum of the values of the corresponding member variables of its arguments. 5. Write the sequence of statements to do the following: i. Declare object obj1 and set its member variables to 5 and 7 respectively ii. Declare object obj2 and set its member variables to 14 and 9 respectively. iii. Create a third object named objR such that the value of each of its member variables is the sum of the values of the corresponding member variables of objects obj1 and obj2 by calling function addDemo2( ). 6. Write a function incrDemo2 that receives as argument an object of the class Demo2 and increments the value of each of its member variables by 5. 7. Write the statement(s) to increment the value of each member variable of object obj1 by 5 by calling function incrDemo2( ). ©2011 Gilbert Ndjatou Page 219 Object-Oriented Programming  Object-Oriented programming is a programming methodology with the following three fundamental characteristics:  Data abstraction and information hiding  Inheritance  Dynamic binding of the messages (function calls) to the methods (definitions of functions) Data abstraction and information hiding  The data is encapsulated with its processing methods (functions) with a controlled access to the data. Inheritance  The definition of a new class (called derived class) can be derived from that of an existing class (called base class).  Inheritance provides an effective way to reuse programming code. Example: the class to represent graduate students can be derived from the class to represent students. Dynamic (run-time) Binding of the Messages to the Methods  Messages (function calls) are dynamically bound to specific method (function) definitions: it means that they are bound during the execution of the program. Data Abstraction and Information Hiding in C++  Data abstraction and information hiding is implemented in C++ by using classes as follows: 1. Make all data members of a class private. 2. For each data member, provide a public member function called set function or mutator that a user of the class must call to modify or set its value. 3. For each data member, provide a public member function called get function or accessor that a user of the class must call to access or obtain its value. ©2011 Gilbert Ndjatou Page 220 Example O1 class Demo3 { public: void readValues(void); // to read the values of the member variables void setValue1(double num); // to set the value of the first member variable void setValue2(double num); // to set the value of the second member variable double getValue1(void); // to return the value of the first member variable double getValue2(void); // to return the value of the second member variable double getAverage( ); // to compute the average of both values private: double computeSum( ); // to compute the sum of both values double val1; // the first member variable double val2; // the second member variable }; /*---------------------------------- function readValues( ) --------------------------------------------------*/ /* read the values of the member variables --------------------------------------------------------------*/ void Demo3:: readValues(void) { cin >> val1 >> val2; } /*---------------------------------- function getValue1( ) --------------------------------------------------*/ /* return the value of the first member variable ------------------------------------------------------*/ double Demo3:: getValue1(void) { return (val1); } /*---------------------------------- function setValue1( ) --------------------------------------------------*/ /* set the value of the first member variable to the given value -------------------------------------*/ void Demo3:: setValue1(double num) { val1 = num; } ©2011 Gilbert Ndjatou Page 221 /*---------------------------------- function getValue2( ) --------------------------------------------------*/ /* return the value of the second member variable --------------------------------------------------*/ double Demo3:: getValue2(void) { return (val2); } /*---------------------------------- function setValue2( ) --------------------------------------------------*/ /* set the value of the second member variable to the given value */ void Demo3:: setValue2(double num) { val2 = num; } /*---------------------------------- function getAverage( ) --------------------------------------------------*/ /* compute the average of both values and return it ----------------------------------------------------*/ double Demo3:: getAverage(void) { double total; total = computeSum( ); return(total / 2); } /*---------------------------------- function computeSum( ) --------------------------------------------------*/ /* compute the sum of both values and return it ----------------------------------------------------------*/ double Demo3:: computeSum(void) { return (val1 + val2 ) ; } /*------ The following code segment defines an object of the class Demo3, reads values for its member variables, and computes and prints their average -----------------*/ Demo3 item1; item1.readValues( ); // read the values for the member variables cout << endl << “The avareage of:\t” << item1.getValue1( ) << “ and “ // output the first value << item1.getValue2( ) << “ is: “ // output the second value << item1.getAverage( ); // output their average ©2011 Gilbert Ndjatou Page 222 /*------ The following code segment defines an object of the class Demo3, sets the values for its members variables to 57 and 86, and computes and prints their average--*/ Demo3 item2; item2.setValue1(57 ); // set the value of the first member variable to 57 item2.setValue2(86 ); // set the value of the second member variable to 86 cout << endl << “The avareage of:\t” << item2.getValue1( ) << “ and “ // output the first value << item2.getValue2( ) << “ is: “ // output the second value << item2.getAverage( ); // output their average Notes 1. You do not have to define a set function for each member variable: this is usually the case when the member variable is initialized or its value is input and will not be modified. 2. A set function may be used to set the values of two or more member variables. For example, the class Demo3 of example O1 could only have one set function setValues (double num1, double num2) that sets the values of both member variables of an object instead of the two set functions setVal1( double num ) and setVal2( double num ). 3. You do not have to define a get function for each member variable: this is usually the case when the value of the member variable is not needed by the user of the class. 4. The essence of object-oriented programming is to solve a problem as follows: a. First identify the real world objects of that problem and the processing required of each object. b. Then create those objects simulations and processes, and the required communications between them. Initializing Object with constructors  A constructor is a special member function of a class that is used to initialize the member variables of the objects of that class.  A constructor of a class has the following characteristics: 1. Its name is the same as the name of the class. 2. It has no return type (not even void). 3. It may or may not have parameters.  A class may have more than one constructor, and  A constructor of a class is automatically called when an object of that class is created. ©2011 Gilbert Ndjatou Page 223 Default Constructor  The default constructor of a class is the constructor with no parameters.  The default constructor of a class is called when an object of that class is defined without initial values.  When you define a class without any constructor, the compiler creates the default constructor for that class.  The default constructor created by the compiler does nothing.  If you define a class with at least one constructor, you must also define the default constructor for that class if you want to define objects of that class without initial value(s): the compiler does not create a default constructor for a class that has another constructor. Example O2 The following class named Demo4 is the class Demo3 of example O1 to which we have added the default constructor. class Demo4 { public: Demo4( ); // default constructor void readValues(void); // to read the values of the member variables void setValue1(double num); // to set the value of the first member variable void setValue2(double num); // to set the value of the second member variable double getValue1(void); // to return the value of the first member variable double getValue2(void); // to return the value of the second member variable double getAverage( ); // to compute the average of both values private: double computeSum( ); // to compute the sum of both values double val1; // the first member variable double val2; // the second member variable }; /*--------------------------Definition of the default constructor-------------------------------------------*/ Demo4 :: Demo4( ) { val1 = 0; val2 = 0; } ©2011 Gilbert Ndjatou Page 224 /*------------------------------ Examples of object definitions----------------------------------------------*/ Demo4 item, // item.val1 is set to 0 and item.val2 is set to 0 stuff; // stuff.val1 is set to 0 and stuff.val2 is set to 0 Constructors with Parameters  The parameter list of a class constructor specifies how the initial values for the member variables of an object of that class must be specified when that object is declared.  When you declare an object, you specify the initial values of its member variables in parentheses following the object‟s name. Example O3 The following class named Demo5 is the class Demo4 of example O2 to which we have added a constructor with parameters. class Demo5 { public: Demo5( ); // default constructor Demo5( double num1, double num2); // constructor with parameters void readValues(void); // to read the values of the member variables void setValue1(double num); // to set the value of the first member variable void setValue2(double num); // to set the value of the second member variable double getValue1(void); // to return the value of the first member variable double getValue2(void); // to return the value of the second member variable double getAverage( ); // to compute the average of both values private: double computeSum( ); // to compute the sum of both values double val1; // the first member variable double val2; // the second member variable }; /*------------------------------Definition of the constructor-------------------------------------------*/ Demo5 :: Demo5( double num1, double num2 ) { val1 = num1; val2 = num2; } ©2011 Gilbert Ndjatou Page 225 /*------------------------------ Examples of object definitions----------------------------------------------*/ Demo5 item1, // item1.val1 is set to 0 and item1.val2 is set to 0 stuff( 10, 15), // stuff.val1 is set to 10 and stuff.val2 is set to 15 obj( -1, 5 ), // obj.val1 is set to -1 and obj.val2 is set to 5 tobj; // tobj.val1 is set to 0 and tobj.val2 is set to 0 Note The following declaration: Demo5 someStuff( ); is the declaration of the function someStuff( ) without parameters, that returns an object of the class Demo5: it is not the definition of the object someStuff with a call to the default constructor. Exercise O1* 1. A class named OurClass has two private data members named first (integer), and second (character). Write the definition of the class OurClass with the following member functions:  The default constructor: it sets the first data member to 0, and the second to „A‟.  The constructor with parameters.  The set functions: setFirst( ) for data member first, and setSecond( ) for data member second.  The get functions: getFirst( ) for data member first, and getSecond( ) for data member second.  The function read( ) that reads the values for the two data members.  The function print( ) that outputs the values of the two data members. 2. Write the following two functions:  Function maxObj( ) that receives as arguments two objects of the class OurClass and returns another object of the class OurClass such that the value of each of its member variables is the maximum value of the corresponding member variables of its arguments.  Function incrObj( ) that receives as argument an object of the class OurClass and add 1 to the value of its first member variable. 3. Write the declaration of the following objects of the class OurClass:  Objects objA and objB with their member variables set to the default values.  Object objC with its member variables set to 100 and „P‟ respectively. 4. Write the statements to do the following: a. Read the values for the two member variables of object objA. b. Set the value of the first member variable of object objB to 15. c. Add 10 to the value of the first member variable of object objA. d. Output the values of the member variables of object objC. e. Call function maxObj( ) with the objects objA and objB as arguments. f. Call function incrObj( ) with object objC as argument. ©2011 Gilbert Ndjatou Page 226 Exercise O2 1. A class named Product has two private data members named unitPrice (double precision value) and quantity (integer value). Write the definition of this class with the following member functions:  The default constructor: it sets the values of both data members to 0.  The constructor with parameters.  The set functions: setUPrice( ) for the unit price, and setQtity( ) for the quantity.  The get functions: getUPrice( ) for the unit price, and getQtity( ) for the quantity.  The function read( ) that reads the values for the unit price and the quantity data members.  The function getPrice( ) that computes and returns the price of the product which is its unit price times its quantity.  The function print( ) that outputs the unit price, the quantity, and the price of the product. 2. Write the following two functions:  Function avgProd( ) that receives as arguments two objects of the class Product and returns another object of the class Product such that the value of unitPrice member variable is the average of the values of the unitPrice member variables of the arguments and the value of the quantity member variable is the sum of the values of the quantity member variables of the arguments.  Function discountProd( ) that receives as argument an object of the class Product and reduces the value of its unitPrice member variable by 10%. 3. Write the declaration of the following objects of the class Product:  Objects itemA and itemB with their member variables set to the default values.  Object itemC with its member variables set to $1.75 and 60 respectively. 4. Write the statements to do the following: a. Read the values for the two member variables of object itemA. b. Set the values of the member variables of object itemB to $2.5 and 100 respectively. c. Add 10 to the value of the quantity member variable of object itemC. d. Output the unit price, the quantity, and the price of object itemC. e. Call function avgProd( ) with objects itemA and itemB as arguments. f. Call function discountProd( ) with object itemC as argument. Copy Constructor and Object Initialization with another Object  The copy constructor of a class is a constructor that has a reference parameter with that class as data type.  The copy constructor of a class copies the values of each member variable of the object that it receives as argument to the corresponding member variable of the object on which it is called. ©2011 Gilbert Ndjatou Page 227 Example O4 The function prototype of the copy constructor of the class Demo5 defined in example O3 follows: Demo5 ( Demo5 & objectInit); It is defined as follows: /*------------------------------Definition of the constructor-------------------------------------------*/ Demo5 :: Demo5( Demo5 & objectInit ) { val1 = objectInit.val1; val2 = objectInit.val2; }  A class copy constructor can be used to initialize an object with another one as follows: Demo5 item( 10, 15 ); Demo5 stuff( item ); // stuff.val1 = item.val1 = 10 and stuff.val2 = item.val2 = 15 With the same effects as the following two statements: Demo5 item( 10, 15 ); Demo5 stuff = item; // stuff.val1 = item.val1 = 10 and stuff.val2 = item.val2 = 15 Note1 Each class that you define in C++ has a default copy constructor created by the compiler: you define a copy constructor for a class only if you do not want to use the one provided by the compiler. Note 2  The copy constructor of a class is called automatically in the following situations: o When a function returns an object of that class. o When an object of that class is passed by value as an argument to a function. ©2011 Gilbert Ndjatou Page 228 Explicit Constructor Call  In C++, a constructor is implicitly a function that returns an object of the class in which it is a member.  A constructor can then be called in the same way that any other function that returns a value (in this case, an object) is called. Example O5 Demo5 item, stuff; item = Demo5 ( ); // calling the default constructor: item.val1 = 0, item1.val2 = 0 stuff = Demo5(9, 20); //calling the constructor with parameters: stuff.val1 = 9, stuff.val2 = 20 Note 3  Since a constructor can be explicitly called to set the values of the member variables of an object, you can define a class with constructors without providing its set functions. Example O6 The following class Demo6 is the class Demo5 of example O3 without the set functions. class Demo6 { public: Demo6( ); // default constructor Demo6( int num1, int num2); // constructor with parameters void readValues(void); // to read the values of the member variables double getValue1(void); // to return the value of the first member variable double getValue2(void); // to return the value of the second member variable double getAverage( ); // to compute the average of both values private: double computeSum( ); // to compute the sum of both values double val1; // the first member variable double val2; // the second member variable };  The constructors of this class will be used to set the values of the two member variables of an object. The only problem with this class is that an object‟s member variables cannot be set individually. ©2011 Gilbert Ndjatou Page 229 The constructors of this class are explicitly called to set the values of the member variables of an object as follows: Demo6 item1, // item1.val1 = 0 itme1.val2 = 0 item2, // item2.val1 = 0 itme2.val2 = 0 item1 = Demo6(6, 4 ); // item1.val1 = 6 itme1.val2 = 4 /*------ read the values for the member variables of object item2 and set them ------------*/ int num1, num2; cin >> num1 >> num2; itme2 = Demo6( num1, num2 ); Exercise O3* Given the following class definition: class MyClass { public: MyClass ( ); // default constructor MyClass ( int num, char symb ); // constructor void process( ); // a member function private: int val; char type; }; Which of the following declarations of objects are invalid? a. MyClass obj1; b. MyClass obj2 ( 34, „A‟ ); c. MyClass obj3 ( ); d. MyClass obj4; obj4 = MyClass ( ); e. MyClass obj5; obj5 = MyClass ( 21, „Z‟); f. MyClass obj6 ( 10, „C‟ ); MyClass obj7 ( obj6 ); g. MyClass obj8 ( 5, „X‟ ); MyClass obj9 = obj8 ; h. MyClass obj10 = MyClass; ©2011 Gilbert Ndjatou Page 230 Exercise O4 Given the following class definition: class YourClass { public: YourClass ( ); // default constructor YourClass ( int num1, double num2 ); // constructor void process( ); // a member function private: int ival; double dval ; }; Which of the following declarations of objects are invalid? a. YourClass obj1; b. YourClass obj2 ( 34, 12.75 ); c. YourClass obj3 ( ); d. YourClass obj4; obj4 = YourClass ( ); e. YourClass obj5; obj5 = YourClass ( 25, 3.87); f. YourClass obj6 ( 10, -5.20 ); YourClass obj7 ( obj6 ); g. YourClass obj8 ( -7, -87.0 ); YourClass obj9 = obj8 ; h. YourClass obj10 = YourClass; Constructors with Default Arguments  A constructor may be specified in a class definition with defaults arguments like any other function.  Using a constructor with default arguments is an alternative way to define a default constructor. Example O7 The following class Demo7 is the class Demo5 of example O3 in which the default constructor and the constructor with parameters are replaced with a constructor with default arguments. ©2011 Gilbert Ndjatou Page 231 class Demo7 { public: Demo7( int num1= 0, int num2 = 0); // constructor with default arguments void readValues(void); // to read the values of the member variables void setValue1(double num); // to set the value of the first member variable void setValue2(double num); // to set the value of the second member variable double getValue1(void); // to return the value of the first member variable double getValue2(void); // to return the value of the second member variable double getAverage( ); // to compute the average of both values private: double computeSum( ); // to compute the sum of both values double val1; // the first member variable double val2; // the second member variable }; /*------------------------------Definition of the constructor-------------------------------------------*/ Demo7 :: Demo7( int num1, int num2 ) { val1 = num1; val2 = num2; } /*------------------------------ Examples of object definitions----------------------------------------------*/ Demo7 item1, // item1.val1 is set to 0 and item1.val2 is set to 0 stuff( 10, 15), // stuff.val1 is set to 10 and stuff.val2 is set to 15 obj( 5 ), // obj.val1 is set to 5 and obj.val2 is set to 0 tobj; // tobj.val1 is set to 0 and tobj.val2 is set to 0 Writing a Constructor with the Initialization Section  An alternative way to write the definition of a constructor is to follow the right parenthesis of the function header with a colon and a list of some or all data members of the class with their initializing expressions in parentheses. Example O8 The following is an alternative way to write the definitions of the constructors of the class Demo5 of example O3. ©2011 Gilbert Ndjatou Page 232 /*------------------------------Definition of the default constructor---------------------------------------*/ Demo5 :: Demo5( ) : val1( 0 ), val2( 0 ) { } /*------------------------------Definition of the constructor with parameters-----------------------------*/ Demo5 :: Demo5( int num1, int num2 ) : val1( num1 ) { val2 = num2; } Exercise O5* 1. Rewrite the definition of the class OurClass that you wrote in exercise O1such that the default constructor and the constructor with parameters are replaced with one constructor with default arguments. 2. Write the definition of the new constructor with the initialization section. Exercise O6 1. Rewrite the definition of the class Product that you wrote in exercise O2 such that the default constructor and the constructor with parameters are replaced with one constructor with default arguments. 2. Write the definition of the new constructor with the initialization section. Data Validation: exit( ) Library Function  It is in general essential to make sure that the value of an object‟s member variable is a valid data before it is assigned to that member variable.  This can be done in a class definition in one of the following two ways: 1. Define a member function that does the data validation and which is called to validate a value before it is assigned to the member variable. 2. Do the data validation in the corresponding set function. In this case, the set function is called by any member function that would like to modify the value of the member variable.  When an invalid data is found, one of the following actions can be taken: 1. Print an error message and then set the value of the member variable to a default value. 2. Print an error message and then call the library function exit( ) to terminate the execution of the program. ©2011 Gilbert Ndjatou Page 233 exit Library Function Prototype: void exit(int status); // Use status 0 if the program has terminated normally; // any other value indicate an error. Header file: Name space: std Operation: terminates the execution of the program. Example O9 The following class DayOfYear has a member function named checkDate( ) that validates a month and a day in a month. This function is called each time the value of the month and/or that of the day data members of the class are set. class DayOfYear { public: DayOfYear(int newMonth = 1, int newDay = 1); // constructor with default arguments void input( ); // to input the month and the day void output( ); // to output the month and the day int getMonth( ); // to return the month int getDay( ); // to return the day private: void checkDate( ); // to validate the month and the day int month; // to hold the month (1 – 12) int day; // to hold the day (1 – 31) }; /*-------------------------------------Definitions of the member functions --------------------------------------*/ #include #include using namespace std; /*----------------------------------------------- Constructor --------------------------------------------------------*/ /* set the month and the day to the provided values and do the data validation */ DayOfYear :: DayOfYear(int newMonth, int newDay) { month = newMonth day = newDay; checkDate( ); } ©2011 Gilbert Ndjatou Page 234 /*-------------------------------------------function input( ) -------------------------------------------------------*/ /* read the month and the day in this order and do the data validation */ void DayOfYear :: input( ) { cin >> month >> day; checkDate( ); } /*-------------------------------------------function output( ) -------------------------------------------------------*/ /* output the month and the day */ void DayOfYear :: output( ) { cout << endl << “month =\t” << month << “\t day =\t” << day; } /*-------------------------------------------function getMonth( ) ------------------------------------------------*/ /* return the month */ void DayOfYear :: getMonth( ) { return ( month); } /*-------------------------------------------function getDay( ) ---------------------------------------------------*/ /* return the day */ void DayOfYear :: getDay( ) { return ( day); } /*-------------------------------------------function checkDate( ) ---------------------------------------------------*/ /* validate the date */ void DayOfYear :: checkDate( ) { if ( (month < 1) || (month > 12) || (day < 1) || (day > 31) ) { cout << endl << “Invalid date”; exit ( 1 ); } } ©2011 Gilbert Ndjatou Page 235 /*--------------------------------------------function main( ) ---------------------------------------------------------*/ /* read a month and a day and find out if it is John Doe’s birth day which is 4/25 */ #include using namespace std; int main( ) { DayOfYear today, johnBirthday; cout << endl << “Enter today\’s date:\t”; today.input( ); cout << endl << “Today\’s date is:\t”; today.output( ); johnBirthday = DayOfYear(4, 25); // set John Doe’s birthday cout << endl << “John\’s birthday is:\t”; johnBirthday.output( ); if (today.getMonth( ) == johnBirthday.getMonth( ) && today.getDay( ) == johnBirthday.getDay( )) cout << endl << “Happy Birthday John Doe”; return 0; } Exercise O7 Define a class named Date with three private data members named month (integer), day (integer), and year (integer) as follows:  This class has a private member function void checkDate( ) that validates a date as follows: - The month must be an integer value from 1 to 12. - The day must be an integer value from 1 to 31. - The year must be an integer value from 1960 to 2011.  Function checkDate( ) calls the library function exit( ) to terminate the program if any of the above conditions is not satisfied.  This class default constructor sets the month data member to 1, the day data member to 1, and the year data member to 1960: The default date is 1/1/1960.  The class constructor with parameters calls function checkDate( ) to check the date after it has set the values for the data members month, day, and year.  The class also has the following public member functions:  void inputDate( ) that reads the values for the data members month, day and year, and then calls function checkDate( ) to check the date.  void outputDate( ) that prints the date in the format: month/day/year.  int getMonth( ), int getDay( ), and int getYear( ). These functions return the value of the month data member, the value of the day data member, and the value of the year data member respectively.  Place the definition of the class in the header file Date.h, and the definitions of the functions in the source file Date.cpp.  Note: the header files iostream, iomanip, cstdlib, and Date.h must be included in the source file Date.cpp. ©2011 Gilbert Ndjatou Page 236 Preprocessor Wrapper  The C++ compiler generates an error message when there is an attempt to include a header file in a source module more than once.  You prevent multiple inclusions of a header file in a source module by using the #ifndef, #define, and #endif preprocessor directives to form a preprocessor wrapper of that header file as follows: #ifndef #define #endif Where is a valid identifier. But in general programmers use the name of the header file in upper case with the period replaced by an underscore. Example #ifndef DAYOFYEAR_H #define DAYOFYEAR_H class DayOfYear { public: DayOfYear(int newMonth = 1, int newDay = 1); // constructor with default arguments void input( ); // to input the month and the day void output( ); // to output the month and the day int getMonth( ); // to return the month int getDay( ); // to return the day private: void checkDate( ); // to validate the month and the day int month; // to hold the month (1 – 12) int day; // to hold the day (1 – 31) }; #endif  If the symbolic constant DAYOFYEAR_H is not yet defined in the source module, then the text between #ifndef (which means “if not defined”) and #endif is inserted into the source module; otherwise, nothing is inserted.  Note that if this code is already inserted in the source module, it will not be inserted the second time; because DAYOFYEAR_H will have already been defined in the source module. ©2011 Gilbert Ndjatou Page 237 Objects as Data Members of another Class  A class can have an object of another class as a data member.  When a class has one or more objects of other classes as data members, it is a good programming practice to initialize these objects in the initialization section of the class constructors.  When an object that is a member of a class is not initialized in the initialization section of the constructors, the default constructor of the class of that object is automatically called to initialize that object. Example O10 As an example of a class with objects of other classes as data members, we define the following class Employee with the following private data members:  first name - class string  last name - class string  birth day - class DayOfYear (of Example O9)  hours - integer  pay rate - double precision In addition to the constructors, the class also has the member functions input( ) that reads the values of an object‟s member variables and print( ) that output the name, birth day and gross pay of an object. class Employee { public: Employee( ); // default constructor Employee( string fname, string lname, DayOfYear bday, int hrs, double prate ); void input( ); // read the values for the data memebers void print( ); // output the values of the data memebers private: string firstName; // first name (object) string lastName; // last name (object) DayOfYear birthDay; // birth day (object) int hours; // number of hours of work double payRate; // Employee’s pay rate }; ©2011 Gilbert Ndjatou Page 238 Note  Objects that are data members of a class are created in the order in which they are declared in the class definition and not in the order in which they appear in the initialization section of constructors. Writing the Default Constructor of the Class Employee:  When you write the default constructor of a class that has one or more objects as data members, you do not have to initialize those objects: each object is initialized by the default constructor of its class when it is not initialized in the initialization section of the constructor.  Two implementations of the default constructor of the class Employee are provided as follows: /*-------------------------------------------default constructor ------------------------------------------------*/ /* initialize member objects firstName and lastName to the null string; the birth day to the default month = 1 and day = 1; and the hours and pay rate to 0 */ /*---------------- Implementation with initialization section -------------------------*/ Employee :: Employee ( ) : hours( 0 ), payRate( 0 ) { } /*-----------------Implementation without initialization section -------------------*/ Employee :: Employee ( ) { hours = 0; payRate = 0; } Writing the Constructor with Parameters of the Class Employee:  When you write a constructor with parameter of a class that has one or more objects as data members, it is a good programming practice to initialize those objects in the initialization section of the constructor: each object is initialized by the default constructor of its class when it is not initialized in the initialization section of the constructor.  Two implementations of the constructor with parameters of the class Employee are provided as follows: ©2011 Gilbert Ndjatou Page 239 /*---------------------Good implementation of the constructor --------------------------------------------------*/ /* use member initializer list to initialize the object data members */ Employee :: Employee( string fname, string lname, DayOfYear bday, int hrs, double prate) : firstName( fname ), // initialize firstName lastName( lname ), // initialize lastname birthDay( bday ), // initialize birthday hours( hrs ), // initialize hours payRate( prate ) // initialize payRate { } /*---------------------Bad implementation of the constructor --------------------------------------------------*/ /*------------------- double initializations of the member objects --------------------------------------------*/ Employee :: Employee( string fname, string lname, DayOfYear bday, int hrs, double prate) { firstName = fname ; // initialize firstName for the second time lastName = lname; // initialize lastname for the second time birthday = bday; // initialize birthday for the second time hours = hrs; // initialize hours payRate = prate; // initialize payRate } Definitions of the other Member Functions: /*---------------------------------- Member function input( ) --------------------------------------------------*/ /* read the values for the member variables */ void Employee :: input( ) { cin >> firstName >> lastName; birthDay.input( ); // read the values for the birth day month and day cin >> hours >> payRate; } ©2011 Gilbert Ndjatou Page 240 /*---------------------------------- Member function print( ) --------------------------------------------------*/ /* output the name, birth day and gross pay of an object */ void Employee :: print( ) { cout << endl << “Name:\t” << lastName + “, “ + firstName; cout << endl << “Birth Day:\t”; birthDay.output( ); // print the values for the birth day month and day cout << endl << “Gross Pay:\t” << ( hours * payRate ); } This class is used in function main as follows:  To read the information about a welder and to compute and print his gross pay.  To compute and print the gross pay of a secretary with the following information: first name: “John”; last name: “Doe”; day of birth: 3/25; hours of work: 35; pay rate: 10.75. /*------read the information about a welder and compute his gross pay and output his information-*/ Employee welder; /*------------------------read his information -----------------------------------------------*/ Welder.input( ); /*------- compute his gross pay and output his information -----------------------------*/ Welder.print( ); /*-----------Define the object secretary and set his information ---------------------------*/ DayOfYear tempday(3, 25); Employee secretary( “John”, “Doe”, tempday, 35, 10.75 ); /*------- compute his gross pay and output his information -----------------------------*/ secretary.print( ); Note: An alternative way to define and initialize object secretary follows: /*-----------Define the object secretary and set his information ---------------------------*/ Employee secretary( “John”, “Doe”, DayOfYear (3, 25), 35, 10.75 ); ©2011 Gilbert Ndjatou Page 241 Exercise O8* 1. Write the definition of the class named Student with the following private data members: first name and last name (class string); ID number (integer) with the default value 999999; birth day (class DayOfYear above); and GPA (double precision value) with the default value 0. In addition to the constructors, it has the public member functions read( ) that inputs the values of an object‟s member variables, and print( ) that outputs the values of an object‟s member variables. 2. Write the definitions of the constructors and the member functions read( ) and print( ). 3. Write the statements to do the following:  define an object of the class Student,  read the values for its member variables and  output the values of its member variables. 4. Define an object of the class Student and initialize its member variables as follows: o First name = Mark o Last name = Depaul o ID number = 1123 o Birth day = 3/25 o GPA = 3.25 5. Output the values of the member variables of the above object. Exercise O9 Using the class Date that you have defined in exercise O7, write the definition of the class named Employee with the following private data members:  first name - class string (the default first name is the null string “ “ )  last name - class string (the default last name is the null string “ “ )  ID number - integer (the default ID number is 999999)  birth day - class Date (the default birth day is the default date: 1/1/1960)  date hired - class Date (the default date of hire is 1/1/20011)  base pay - double precision (the default base pay is $0.00) In addition to the constructors, the class has the following public member functions:  void readPInfo( ) that reads the values for the data members first name, last name, ID number, birth day, and date of hire.  void readPayInfo( ) that reads the value for the base pay data member.  void printPInfo( ) that outputs the values of the data members first name, last name, ID number, birth day, and date of hire.  void setBpay( double newBpay ) that sets the value of the base pay to the new value, newBpay.  double getBpay( ) that returns the value of the base pay data member.  double getGpay( ) that returns the value of the gross pay (which is the base pay).  double computeTax( ) that computes the tax deduction on the gross pay and returns it as follows: ©2011 Gilbert Ndjatou Page 242 If gross pay is greater than or equal to 1000, 20% of the gross pay; If 800 <= gross pay < 1000, 18% of gross pay If 600 <= gross pay < 800, 15% of gross pay Otherwise, 10 % of the gross pay.  void printPayInfo( ) that outputs the gross pay, tax deduction, and net pay (gross pay - tax deduction).  Place the definition of this class in the header file Employee.h, and the definitions of the member functions in the source file Employee.cpp.  Note: - the header files string and Date.h must be included in the header file Employee.h and the header file Employee.h must be included in the source file Employee.cpp. - The header file Employee.h must look like the following: #ifndef EMPLOYEE_H #define EMPLOYEE_H #include using namespace std; #include “Date.h” Enter the class here #endif ©2011 Gilbert Ndjatou Page 243 Inheritance  Inheritance is the process by which one class called derived class is created from an existing class called base class.  The base class is sometime called parent class or superclass whereas the derived class is sometime called child class or subclass.  The definition of a derived class begins like any other class definition, but the name of the class is followed by a colon, then an access-specifier (public/protected/private) and the name of the base class. Example O11 Definition of the Base class: class Parent { public: Parent( ); // default constructor Parent( int n ); // constructor void setValue1( int n ); int getValue1( ); void print( ); // print the value of the data member private: int num1; }; /*----------------------------- Default constructor ----------------------------------------*/ Parent :: Parent( ) : num1( 0 ) { } /*----------------------------- Constructor with parameters ------------------------------*/ Parent :: Parent( int n ) : num1( n ) { } ©2011 Gilbert Ndjatou Page 244 /*-------------------------------------set function---------------------------------------------*/ void Parent :: setValue1( int n ) { num1 = n; } /*-------------------------------- get function -------------------------------------------------*/ int Parent :: getValue1( void ) { return ( num1 ); } /*------------------------------------------print function ----------------------------------------*/ void Parent :: print( ) { cout << endl << “num1 =” << num1; } Definition of the Derived Class: class Child : public Parent // inherits class Parent { public: Child( ); // default constructor Child ( int n1, int n2 ); // constructor void setValue2( int n ); int getValue2( ); void print( ); // print values of both data members private: int num2; }; ©2011 Gilbert Ndjatou Page 245  Class Child is viewed by the system as if it was defined as follows: class Child { public: Child( ); // default constructor Child ( int n1, int n2 ); // constructor void setValue1( int n ); int getValue1( ); void setValue2( int n ); int getValue2( ); void print( ); // print values of both data members private: int num1; int num2; }; However, inherited private data member num1 is not directly accessible in class Child. Constructors of a Derived Class  The constructors of the base class are not inherited in a derived class.  The constructors of the base class are invoked (called) in the initialization section of the constructors of a derived class to initialize the inherited data members.  The constructors of the class Child above are defined as follows: /*----------------------Default constructors of the derived class Child ------------------------------*/ Child :: Child( ) : Parent( ) // call of base class default constructor: num1 = 0 { num2 = 0; } /*----------------------Constructor with parameters of the derived class Child --------------------------*/ Child :: Child( int n1, int n2 ) : Parent( n1 ) // call of base class constructor: num1 = n1 { num2 = n2; } ©2011 Gilbert Ndjatou Page 246 Public Member Functions and Data Members of the Base Class  A public data member of a public base class becomes a public data member of a derived class.  A public member function of a public base class becomes a public member function of a derived class if it is not redefined in that derived class.  When a public member function of the base class is redefined in a derived class, any call of that function on an object of the derived class will invoked the definition of the function in the derived class. Example  The public member functions setValue1( ) and getValue1( ) of the base class Parent are also public member functions of the derived class Child.  The public member function print( ) of the base class Parent is not a member function of the derived class Child because this function is redefined in the derived class Child. Private Member Functions and Data Members of the Base Class  A private member function of a public base class is not accessible in a member function of a derived class.  A private data member of a public base class becomes a private data member of a derived class but it is not directly accessible in a member function of the derived class: it can be accessed only by using a get or a set function. Example Private data member num1 of the base class Parent can only be accessed in the member function print of the derived class Child through the get function, getValue1( ) as follows: void Child :: print( ) { cout << endl << “num1 =” << getValue1( ) ; cout << endl << “num2 =” << num2; } ©2011 Gilbert Ndjatou Page 247 Exercise O10* Assume given the following class definition: class Item { public: Item ( ); //default name is “ “ and default quantity is 0 Item ( string itsname, int qtity ); void read( ); // read the name and the quantity of an item void setName( string newName ); // set the new name of an item void setQtity( int newQtity); // set the new quantity of an item string getName( ); // returns the name of an item int getQtity( ); //returns the quantity of an item void print( ); // prints the name and the quantity of an item private: string name; int quantity; }; 1. Write the definitions of the constructors and the other member functions. 2. Write the definition of the derived class of class Item named Item4Sale as follows: a. It has an additional private data member named unitPrice (double precision value). b. In addition to the constructors, it has the following public member functions:  double getUnitPrice( ) that returns the value of the data member unitPrice.  void setUnitPrice( double uprice ) that sets the new value of the unit price. c. Member function void read( ) is redefined in the class Item4Sale. It reads the unit price in addition to the name and the quantity of an item. d. Member function void print( ) is redefined in the class Item4Sale. It prints the unit price and the price of an item (the unit price times the quantity) in addition to the name and the quantity. 3. List the following: a. All member functions of class Item4Sale (each one with its access-specifier and description). b. All data members of the class Item4Sale. List each one with its access-specifier and also indicate whether or not it is accessible in a new/redefined member function of class Item4Sale. 4. Write the definitions of the constructors (the default unit price is $1.00), the functions read( ) and print( ), and the new member functions. 5. Assume given the following definitions of objects t1 and t2: Item t1(“Apple”, 25); Item4Sale t2(“Orange”, 34, 0.20); What is the output produced by the following two statements: t1.print( ); t2.print( ); ©2011 Gilbert Ndjatou Page 248 Exercise O11 Assume given the following class definition: class RectangularLot { public: RectangularLot( ); //default length is 1 and default width is 1 RectangularLot( double len, double wid ); void read( ); // read the length and the width of the lot void setLength( double len); // set the new value of the data member length void setWidth( double wid ); // set the new value of the data member width double getLength( ); // returns the length of the lot double getWidth( ); //returns the width of the lot double getArea( ); // computes and returns the area of the lot void print( ); // prints the length, the width and the area of the lot private: double length; double width; }; 1. Write the definitions of the constructors and the other member functions of this class. 2. Write the definition of the derived class of class RectangularLot named Lot4Sale as follows: a. It has an additional private data member named unitPrice (double precision value). b. In addition to the constructors, it has the following public member functions:  double getUnitPrice( ) returns the value of the data member unitPrice.  void setUnitPrice( double uprice ) sets the new value of the unit price.  double getPrice( ) returns the price of the lot (the unit price times the area). c. Member function void read( ) is redefined in class Lot4Sale. It reads the unit price in addition to the length, and the width. d. Member function void print( ) is redefined in class Lot4Sale. It prints the unit price and the price of the lot (the unit price times the area) in addition to the length, the width, and the area. 3. List the following: a. All member functions of class Lot4Sale (each one with its access-specifier and its description). b. All data members of class Lot4Sale. List each one with its access-specifier and also indicate whether or not it is accessible in a new/redefined member function of class Lot4Sale. 4. Write the definitions of the constructors (the default unit price is $1000.00), the functions read( ) and print( ), and the new member functions of the class Lot4Sale. 5. Assuming that objects lot1 and lot2 are defined as follows: RectangularLot lot1( 80.00, 55); Lot4Sale lot2( 120, 50, 5000.00); What is the output produced by the following two statements: lot1.print( ); lot2.print( ); ©2011 Gilbert Ndjatou Page 249 Exercise O12 Write the definition of the derived class of class Employee (that you have defined in exercise O9) named BonusEmployee as follows: 1. It has one additional private data members named bonus (double precision) with the default value $0.0. 2. In addition to the constructors, it has the public member function: double getBonus( void ) that returns the value of the data member bonus. 3. Member function void readPayInfo( ) is redefined in the class BonusEmploye: it now reads the values for the data members base pay and bonus. 4. Member function double getGpay( ) is redefined in the class BonusEmploye: it now returns the value of the data member base pay plus the value of the data member bonus. 5. Member function double computeTax( ) is redefined in the class BonusEmploye: It now calls the redefined member function getGpay( ) to get the gross pay and then computes the tax deduction in the same way as in exercise O9. 6. Member function void printPayInfo( ) is redefined in the class BonusEmploye: it now prints the values of the data members bonus and base pay, in addition to the gross pay, tax deduction, and net pay. 7. Place the definition of this class in the header file BonusEmploye.h and the definitions of the member functions in the source file BonusEmploye.cpp. 8. Note: the header file Employee.h must be included in the header file BonusEmploye.h. ©2011 Gilbert Ndjatou Page 250 Exercise O13 Extra Credit Write the definition of the derived class of class Employee (that you have defined in exercise O9) named HourlyEmployee as follows: 1. It has three additional private data members named hours (integer) and payRate (double precision), and overtime (double precision). Their default values are 0 for hours, and $0.00 for payRate and overtime. 2. It also has a private member function void computeBaseOvertimePay( ) that computes the base pay and the overtime pay as follows: a. If the value of the data member hours is less than or equal to 35, then it does the following: i. Set the value of the inherited data member base pay to payRate times hours. ii. Set the value of the data member overtime to 0.00. b. Otherwise, it does the following: i. Set the value of the inherited data member base pay to payRate times 35. ii. Set the value of the data member overtime to payRate times 1.5 times (hours – 35). 3. The constructor with parameters has the following function header: HourlyEmployee( string fn, string ln, int iD, Date bd, Date hd, int hrs, double prate) Where hrs represents the number of hours of work and prate the pay rate. It calls class Employee’s constructor with 0 as the argument for the data member base pay, and then calls the private member function computeBaseOvertimePay( ) to set the values of the data members base pay and overtime. 4. In addition to the constructors, it has the following public member functions: a. int getHours( void ) returns the value of the data member hours. b. double getPayRate( void ) returns the value of the data member payRate. c. double getOvertime( void ) returns the value of the data member overtime. 5. Member function void readPayInfo( ) is redefined in the class HourlyEmployee: it now reads the values of the data members hours and payRate, and then calls the private member function computeBaseOvertimePay( ) to set the values of the data members base pay and overtime. 6. Member function double getGpay( ) is redefined in the class HourlyEmployee: it now returns the sum of the values of the data members base pay and overtime. 7. Member function double computeTax( ) is redefined in the class HourlyEmployee: It now calls the redefined member function getGpay( ) to get the gross pay and then computes the tax deduction in the same way as in exercise O9. 8. Member function void printPayInfo( ) is redefined in the class HourlyEmployee: it now outputs the values of the data members hours, payRate, base pay, and overtime, in addition to the gross pay, tax deduction, and net pay. 9. Place the definition of this class in the header file HourlyEmployee.h and the definitions of the member functions in the source file HourlyEmployee.cpp. 10. Note: the header files Employee.h must be included in the header file HourlyEmployee.h. ©2011 Gilbert Ndjatou Page 251 Accessing a Redefined Member Function of the Base Class  In C++, you can call a member function of the base class (that is redefined in a derived class) in the definition of a member function of that derived class.  You do this by preceding the function call with the name of the base class followed by the scope resolution operator. Example Given the base class Parent and the derived class Child of example O11, member function print( ) that is redefined in the derived class Child can be rewriting by calling the member function print( ) of the base class Parent as follows: void Child :: print( ) { Parent :: print( ) ; // print the first data member cout << endl << “num2 =” << num2; // print the second data member }  In C++, you can call a member function of the base class (that is redefined in a derived class) on an object of that derived class by preceding the function call with the name of the base class followed the scope resolution operator.  The object of a derived class on which a member function of the base class (that is redefined in the derived class) is called, is treated as an object of the base class. Example Given the base class Parent and the derived class Child of example O11 and the following declarations of objects: Parent pOject( 5 ); Child cObject( 2, 3); The statement will produce the following output pObject.print( ); num1 = 5 cObject.print( ); num1 = 2 num2 = 3 cObject.Parent :: print ( ); num1 = 2 ©2011 Gilbert Ndjatou Page 252 Exercise O14* In exercise O10, member functions void read( ) and void print( ) of the base class Item are redefined in the derived class Item4Sale. 1. Write a new definition of the member function read( ) in which there is a call to the member function read( ) of the base class Item and a new definition of the member function print( )in which there is a call to the member function print( ) of the base class Item. 2. Given the following definitions of objects t1, t2, and t3: Item t1( “Apple”, 25); Item4Sale t2(“Banana”, 50, .10), t3; a. What is produced by the following output statements: t1.print( ); t2.print( ); t2.Item :: print( ); b. Write a statement to read the name and the quantity of object t3 by calling the read( ) member function of the base class Item. Exercise O15 In exercise O11, member functions void read( ) and void print( ) of the base class RectangularLot are redefined in the derived class Lot4Sale. 1. Write a new definition of the member function read( ) in which there is a call to the member function read( ) of the base class RectangularLot and a new definition of the member function print() in which there is a call to the member function print( ) of the base class RectangularLot. 2. Given the following definitions of objects lot1,lot2, and lot3: RectangularLot lot1( 80, 25); Lot4Sale lot2(100, 50, 10000), lot3; a. What is produced by the following output statements: lot1.print( ); lot2.print( ); lot2.RectangularLot :: print( ); b. Write a statement to read the length and the width of object lot3 by calling the read( ) member function of the base class RectangularLot. ©2011 Gilbert Ndjatou Page 253 Exercise O16 In exercise O12, member functions void readPayInfo( ) of the base class Employee is redefined in the class BonusEmployee. 1. Write a new definition of the member function readPayInfo( ) in which there is a call to the member function readPayInfo( ) of the base class Employee. 2. Given the following definitions of objects emp1,emp2, and emp3: Employee emp1( “John”, “Doe”, 111111, Date(10, 25, 1991), Date(5, 10, 2010), 1250); BonusEmployee emp2( “Job”, “Daly”, 222222, Date(1, 5, 1990), Date(6, 20, 2011), 850, 250), emp3; a. What is produced by the following output statements: emp1.printPayInfo( ); emp2.printprintPayInfo( ); emp2.Employee :: printPayInfo( ); b. Write a statement to read the base pay of object emp3 by calling the readPayInfo( ) member function of the base class Employee. Protected members of a Class  When you write the definition of a class, you can make a member function or a data member of that class a protected member by preceding its declaration/definition with the label protected: instead of the label private:  A protected data member/member function of a base class is like a private data member/member function of that class except that it can be directed accessed in a member function of a derived class. Example If we redefine the base class Parent of example O11 as follows: class Parent { public: Parent( ); // default constructor Parent( int n ); // constructor void setValue1( int n ); int getValue1( ); void print( ); // print the value of the member variable protected: int num1; }; ©2011 Gilbert Ndjatou Page 254 Then we can now access the protected data member num1 in the member function print( ) of the derived class Child as follows: void Child :: print( ) { cout << endl << “num1 =” << num1; cout << endl << “num2 =” << num2; } Exercise O17* Assuming that the private data members name and quantity of the class Item defined in exercise O10 are protected data members, rewrite the definitions of the member functions void read( ) and void print( ) that are redefined in the class item4Sale. Exercise O18 Assuming that the private data members length and width of the class RectangularLot defined in exercise O11 are protected data members, rewrite the definitions of the member functions void read( ) and void print( ) that are redefined in the class Lot4Sale. Exercise O19 Assuming that the private data member base pay of the class Employee defined in exercise O9 is a protected data member, rewrite the definitions of the member functions void readPayInfo( ), double getGpay( ), and void printPayInfo( ) that are redefined in the class BonusEmploye. Data Type of an Object of a Derived Class  An object of a derived class is also an object of the base class (without the additional data members and member functions):  It can be used anywhere (such as arguments to functions) that an object of its base class is allowed.  It can also be assigned to an object of the base class.  However, an object of the base class is not an object of a derived class. ©2011 Gilbert Ndjatou Page 255 Example Given the base class Parent and the derived class Child of example O11, the following function definition: void funct( Parent obj ) { cout << 10 * obj.getValue1( ); } And the following definitions of objects: Parent pobj1( 2 ) , pobj2; Child cobj1( 3, 4 ) , cobj2; The following assignment statement is legal: pobj2 = cobj1; // pobj2.num1 is set to 3 The following assignment statement is illegal: cobj2 = pobj1. // you cannot assign an object of the base class to an object of a derived class The following call statements are legal: funct( pobj1 ); // output will be: 20 funct( cobj1 ); // output will be: 30 Exercise O20* Using the definitions of the classes Item and Item4Sale of exercise O10, we define function helper( ) as follows: void helper ( Item t ) { t.print ( ); } And the object t1, t2, and t3 as follow: Item t1( “Pie”, 60 ), t2; Item4Sale t3( “hat”, 100, 30.00); ©2011 Gilbert Ndjatou Page 256 Execute the following statements and show their output: a. t1.print( ); b. t3.print( ); c. helper ( t1 ); d. helper ( t3 ); e. t2 = Item4Sale( “Shirt”, 150, 10.0 ); t2.print( ); Exercise O21 Using the definitions of the classes RectangularLot and Lot4Sale of exercise O11, we define function helper( ) as follows: void helper ( RectangularLot lot ) { lot.print ( ); } And the object myLot, yourLot, and hisLot as follow: RectangularLot myLot( 30, 200 ), hisLot; Lot4Sale yourLot ( 50, 100, 2000); Execute the following statements and show their output: a. myLot.print( ); b. yourLot.print( ); c. helper ( myLot ); d. helper ( yourLot ); e. hisLot = Lot4Sale( 40, 150, 3000 ); hisLot.print( ); ©2011 Gilbert Ndjatou Page 257 Virtual Functions: Dynamic/Late Binding  A function of the base class that will be redefined in derived classes can be made a virtual function by adding the keyword virtual to its function prototype in the base class definition.  It is necessary to make a function of a base class a virtual function in the following situation: functA( ) and functB( ) are member functions of a base class such that:  Member function functA is called in member function functB( ).  Member function functA is redefined in a derived class.  Member function functB is not redefined in that derived class.  When member function functB( ) is called on an object of the base class, we want the definition of the member function functA( ) in the base class to be used in the function call, and  When member function functB( ) is called on an object of the derived class, we want the definition of the member function functA( ) in the derived class to be used in the function call  This can only be done by making member function functA( ) a virtual function.  Note that if you do not want to make member function functA( ) a virtual function, you will have to redefine member function functB( ) in all derived classes as we did for the member function computeTax( ) of the classes Employee of exercise O9, BonusEmployee of exercise O12 and HourlyEmployee of exercise O13. By doing this, the definition of member function functA( )in each class is bound to the function call in the member function functB( ) defined in that class.  By making a member function of a base class a virtual function, you are saying to the compiler that it should not use the definition of that function that is provided in the base class when it is processing that function call: the binding of the function call to the proper definition of the virtual function must be delayed until the function that call the virtual function is called in the program: C++ chooses the definition of the virtual function that corresponds to the object been processed.  Delaying the binding of a virtual function call to its definition is referred to as late binding.  A late binding is referred to as dynamic binding if it occurs during the execution of the program. Note  The definition of a virtual function in a base class serves as a default definition: It will be used on objects of a derived class only if its definition is not overridden in that derived class. Example O12 A company sales two shapes of tiles (rectangular, and triangular) and the price of a tile is the unit price per square inch times the area of the tile. To process the information about these tiles, we design a base class named Tile to represent the information common to all tiles and then create derived classes RectangleTile and TriangleTile to represent the information about each shape of tile as follows: ©2011 Gilbert Ndjatou Page 258 class Tile { public: Tile( ); Tile( double uprice ); double getUprice( ); virtual double computeArea( ); //a place holer function double computePrice( ); void print( ); private: double unitPrice; }; /*-------------------------------- Definition of the default constructor -------------------------*/ Tile :: Tile( ) : unitPrice ( 2.0 ) { } /*-------------------------------- Definition of the constructor with parameters -------------------------*/ Tile :: Tile ( double uprice ) : unitPrice( uprice ) { } /*-------------------------------- Definition of member function getUprice( ) -------------------------*/ double Tile :: getUprice( void ) { return unitPrice ; } /*-------------------------------- Definition of member function computeArea( ) -------------------------*/ double Tile :: computeArea( void ) { return ( 1 ); // return a dummy area of 1sqrt inch } /*------------------------------ Definition of member function computePrice( ) -------------------------*/ double Tile :: computePrice( ) { double area; area = computeArea( ); // call to the virtual function compute Area is delayed return( unitPrice * area ); } ©2011 Gilbert Ndjatou Page 259 Note Although member function computeArea( ) is not needed in the class Tile, we need its definition in order to write the definition of member function computePrice( ). /*-------------------------------- Definition of member function print( ) -------------------------*/ void Tile :: print( void ) { cout << endl << “The price of the tile is:\t” << computePrice ( ); } Derived Classes: class RectangleTile : public Tile // inherits class Tile { public: RectangleTile ( ); // default constructor RectangleTile ( double uprice , double len , double wth); // constructor virtual double computeArea( ); // function to be called for Rectangle objects void print( ); private: double length; double width; }; /*-------------------------------- Definition of the default constructor -------------------------*/ RectangleTile :: RectangleTile( ) : Tile( ) , length( 0.5 ) , width( 1.0 ) { } /*-------------------------------- Definition of the constructor with parameters -------------------------*/ RectangleTile :: RectangleTile(double len , double wth, double uprice ):Tile( uprice ) , length( len ) , width( wth ) { } /*-------------------------------- Re-definition of member function computeArea( ) -------------------------*/ double RetangleTile :: computeArea( void ) { return ( length * width ); // return the area of a rectangular tile } ©2011 Gilbert Ndjatou Page 260 /*-------------------------------- Re-definition of member function print( ) -------------------------*/ void RectangleTile :: print( void ) { cout << endl << “The length is:\t” << length << endl << “The width is:\t” << width; cout << endl << “The price of the tile is:\t” << computePrice ( ); } class TriangleTile : public Tile // inherits class Tile { public: TriangleTile ( ); // default constructor TriangleTile (double ht , double bse, double uprice ); // constructor virtual double computeArea( ); // function to be called for triangle objects void print( ); private: double height; double base; }; /*-------------------------------- Definition of the default constructor -------------------------*/ TriangleTile :: TriangleTile ( ) : Tile( ) , height( 0.5 ) , base( 1.0 ) { } /*-------------------------------- Definition of the constructor with parameters -------------------------*/ TriangleTile :: TriangleTile (double ht , double bse, double uprice ) : Tile( uprice ) , height( ht ) , base( bse ) { } /*-------------------------------- Redeefinition of member function computeArea( ) -------------------------*/ double TriangleTile :: computeArea( void ) { return ( height * base / 2.0 ); // return the area of a rectangular tile } ©2011 Gilbert Ndjatou Page 261 /*-------------------------------- Re-definition of member function print( ) -------------------------*/ void TriangleTile :: print( void ) { cout << endl << “The height is:\t” << height << endl << “The base is:\t” << base; cout << endl << “The price of the tile is:\t” << computePrice ( ); } Exercise O22* Given the following definitions of objects, Tile obj1, obj2( 10.0 ); RectangleTile robj1, robj2( 3.0, 5.0, 4.0 ); Show the following outputs: a. obj1.print( ); b. obj2.print ( ); c. robj1.print( ); d. robj2.print( ); Exercise O23 Given the following definitions of objects, Tile obj1(5.0), obj2 (20.0 ); TriangleTile tobj1, tobj2( 2.0, 6.0, 8.0 ); Show the following outputs: a. obj1.print( ); b. obj2.print ( ); c. tobj1.print( ); d. tobj2.print( ); Exercise O24 1. Modify class Employee that you have defined in exercise O9 by making the member function double getGpay( ) a virtual function. 2. With this modification of the class Employee, explain why you do not need to redefine the member function double computeTax( ) in the class BonusEmployee. 3. Assuming that member function double getGpay( ) is a virtual member function of the class Employee, rewrite the definition of the class BonusEmploye without redefining the member function double computeTax( ) of the base class Employee. ©2011 Gilbert Ndjatou Page 262 Exercise O25 Extra Credit Assuming that member function double getGpay( ) is a virtual member function of the class Employee, rewrite the definition of the class HourlyEmployee without redefining the member function double computeTax( ) of the base class Employee. Pure Virtual Functions and Abstract Classes  A virtual member function of a base class whose definition is not needed in that class can be made a pure virtual function by following its function prototype in the class definition with the expression: = 0.  Note that you do not have to write the definition of a pure virtual function in the base class: its definitions are provided in the derived classes of the base class.  A class with one or more pure virtual functions is referred to as an abstract base class.  An abstract base class cannot be used to instantiate objects. Example The base class Tile of example O12 can be rewritten by making the member function double computeArea( ) a pure virtual function as follows: class Tile { public: Tile( ); Tile( double uprice ); double getUprice( ); virtual double computeArea( ) = 0 ; //a place holer function double computePrice( ); void print( ); private: double unitPrice; }; ©2011 Gilbert Ndjatou Page 263 Polymorphic Functions  A polymorphic function is a function that behaves in different ways for different kinds of objects.  A virtual function can be used to create a polymorphic function as in the following example: Example O13 Assume given the class Tile and its derived classes RectangleTile and TriangleTile of example O12 with the following modification: member function print( ) is now a virtual function and a new member function void readDimensions( ) is added. class Tile { public: Tile( ); Tile( double uprice ); double getUprice( ); virtual void readDimensions( ) = 0; // a place holder function to read the dimensions of a tile virtual double computeArea( ); //default definition of member function computeArea( ) double computePrice( ); virtual void print( ); private: double unitPrice; }; /*-------------------------------- Definition of constructors and member functions -------------------------*/ Tile :: Tile( ) : unitPrice ( 2.0 ) { } Tile :: Tile ( double uprice ) : unitPrice( uprice ) { } double Tile :: getUprice( void ) { return unitPrice ; } double Tile :: computeArea( void ) { return ( 1 ); // return a dummy area of 1sqrt inch } ©2011 Gilbert Ndjatou Page 264 double Tile :: computePrice( ) { double area; area = computeArea( ); // call to the virtual function compute Area is delayed return( unitPrice * area ); } void Tile :: print( void ) { cout << endl << “The price of the tile is:\t” << computePrice ( ); } Derived Class RectangleTile: class RectangleTile : public Tile // inherits class Tile { public: RectangleTile ( ); // default constructor RectangleTile ( double uprice , double len , double wth); // constructor virtual double computeArea( ); // function to be called for Rectangle objects virtual void print( ); private: double length; double width; }; /*-------------------------------- Definition of constructors and member functions -------------------------*/ RectangleTile :: RectangleTile( ) : Tile( ) , length( 0.5 ) , width( 1.0 ) { } RectangleTile :: RectangleTile(double len , double wth, double uprice ):Tile( uprice ) , length( len ) , width( wth ) { } double RetangleTile :: computeArea( void ) { return ( length * width ); // return the area of a rectangular tile } ©2011 Gilbert Ndjatou Page 265 void RectangleTile :: print( void ) { cout << endl << “The length is:\t” << length << endl << “The width is:\t” << width; cout << endl << “The price of the tile is:\t” << computePrice ( ); } Derived Class TriangleTile: class TriangleTile : public Tile // inherits class Tile { public: TriangleTile ( ); // default constructor TriangleTile (double ht , double bse, double uprice ); // constructor virtual double computeArea( ); // function to be called for triangle objects virtual void print( ); private: double height; double base; }; /*-------------------------------- Definition of constructors and member functions -------------------------*/ TriangleTile :: TriangleTile ( ) : Tile( ) , height( 0.5 ) , base( 1.0 ) { } TriangleTile::TriangleTile (double ht , double bse, double uprice ):Tile( uprice) , height( ht) , base(bse ) { } double TriangleTile :: computeArea( void ) { return ( height * base / 2.0 ); // return the area of a rectangular tile } void TriangleTile :: print( void ) { cout << endl << “The height is:\t” << height << endl << “The base is:\t” << base; cout << endl << “The price of the tile is:\t” << computePrice ( ); } ©2011 Gilbert Ndjatou Page 266 Given the following definition of function helper( ): void helper( const Tile & obj ) { obj.print( ); } And the following definitions of objects: RectangleTile item2( 5.0, 3.0, 2.0); TriangleTile item3( 4.0, 6.0, 1.0 ); The execution of the following statements will produce the following output: helper( item2 ); cout << endl; helper( item3 ); cout << endl; OUTPUT The length is: 5.0 The width is: 3.0 The price of the tile is: 30.0 The height is: 4.0 The base is: 6.0 The price of the tile is: 12.0 Note: Function helper ( ) is a polymorphic function: it behaves in different ways for different kinds of objects. ©2011 Gilbert Ndjatou Page 267  friend Functions  An ordinary function that has an object of a class as a parameter or that processes an object of a class as a local/global variable can be made a friend function of that class.  The only purpose of making an ordinary function a friend function of a class is for that function to have access to the private data members and member functions of that class.  You make an ordinary function a friend function of a class by preceding its prototype in that class definition with the keyword friend.  This declaration may appear in any section (private/public) of a class definition. Example O14 Given the following definition of class Demo8: class Demo8 { public: Demo8(int n1 = 0, int n2 = 0); // constructor int getFirst( ); // returns the value of the first member variable int getSecond( ); // returns the value of the second member variable private: int val1; int val2; }; Function addDemo8( Demo8 ob1, Demo8 obj2) that receives as arguments two objects of the class Demo8 and returns another object of the class Demo8 such that the value of each of its member variables is the sum of the values of the correspond member variables of the objects that it receives as arguments and function updateDemo8( Demo8 &obj) that receives as argument an object of the class Demo8 and adds 1 to the value of each of its member variables are defined as ordinary functions as ordinary functions as follows: /*----------------------------------------function addDemo8( ) ----------------------------------------------------*/ /* receives two objects of the class Demo8 and returns another object of the same class with each member variable the sum of thevalues of the corresponding member variables of both objects */ Demo8 addDemo8( Demo8 obj1, Demo8 obj2) { Demo8 objResult; int num1 = obj1.getFirts( ) + obj2.getFirst( ); int num2 = obj1.getSecond( ) + obj2.getSecond( ); objResult = Demo8( num1, num2 ); return ( objResult); } ©2011 Gilbert Ndjatou Page 268 /*----------------------------------------function updateDemo8( ) -----------------------------------------------*/ /* receives an object of the class Demo8 and adds 1 to the value of each of its member variables */ void updateDemo8( Demo8 &obj ) { int num1 = obj.getFirst( ) ; int num2 = obj.getSecond( ) ; obj = Demo8( num1+1, num2+1 ); } These two functions are defined as friend functions of the class Demo8 as follows: class Demo8 { public: Demo8(int n1 = 0, int n2 = 0); // constructor int getFirst( ); // returns the value of the first member variable int getSecond( ); // returns the value of the second member variable friend Demo8 addDemo8( Demo8 ob1, Demo8 obj2); friend void updateDemo8( Demo8 &obj); private: int val1; int val2; }; /*----------------------------------------function addDemo8( ) ----------------------------------------------------*/ /* receives two objects of the class Demo8 and returns another object of the same class with each member variable the sum of the corresponding member variables of both objects */ Demo8 addDemo8( Demo8 obj1, Demo8 obj2) { Demo8 objResult; objResult.val1 = obj1.val1 + obj2.val1; objResult.val2 = obj1.val2 + obj2.val2; return ( objResult); } /*----------------------------------------function updateDemo8( ) --------------------------------------------------*/ /* receives an object of the class Demo8 and increments each of its member variables by 1 */ void updateDemo8( Demo8 &obj ) { obj.val1 ++ ; obj.val2 ++ ; } ©2011 Gilbert Ndjatou Page 269 /*---------------------- calling functions addDemo8( ) and updateDemo8( ) ---------------------------------*/ Demo8 tobj(14, 25), sobj(5, 9), robj; robj = addDemo8 ( tobj, sobj ); cout << endl << “first value is:\t” << robj.getFirst( ) << endl << “second value is:\t” << robj.getSecond( ); updateDemo8 ( tobj ); cout << endl << “first value is:\t” << tobj.getFirst( ) << endl << “second value is:\t” << tobj.getSecond( ); Exercise O26 Given the following definition of class Demo8: class Demo8 { public: Demo8(int n1 = 0, int n2 = 0); // constructor int getFirst( ); // returns the value of the first member variable int getSecond( ); // returns the value of the second member variable private: int val1; int val2; }; Function subDemo8( Demo8 ob1, Demo8 obj2) receives as arguments two objects of the class Demo8 and returns another object of the class Demo8 such that the value of each of its member variables is the difference of the value of the corresponding member variable of the first object minus the value of the corresponding member variable of the second object that it receives as arguments and function decDemo8( Demo8 &obj) receives as argument an object of the class Demo8 and subtracts 1 from the value of each of its member variables. 1. Provide the definitions of these two functions as ordinary functions. 2. Provide the definitions of these two functions as friend functions of the class Demo8. 3. Given the following objects: Demo8 obj1( 5, 8), obj2( 12, 21), obj3( 9, 6), obj4; Write the statements to assign values the member variables of object obj4 such that the value of each member variable is the difference of the value of the corresponding member variable of object obj1 minus the value of the corresponding member variable of object obj2 (by calling function subDemo8( )). Also write the statements to decrement the value of each member variable of object obj3 by 1 (by calling function decDemo8( )). ©2011 Gilbert Ndjatou Page 270 Solution Exercises Exercise C1 a. void Automobile : : setPrice( double newPrice ) { price = newPrice; } void Automobile : : setProfit( double newProfit ) { profit = newProfit; } double Automobile : : getPrice( ) { return price; } double Automobile : : getProfit( ) { return profit; } b. Invalid Statement Reasons hyunday.price = 15000.00; price is a private data member of the class cout << jaguar.getProfit ( ); getProfit( ) is a private member function of the class jaguar.setProfit( ); The class member function setProfit( ) is called without an argument setPrice ( 16500 ); The class member function setPrice( ) is not called on an object a. jaquar.setProfit( 3500 ); b. double carPrice; cin >> carPrice; hynday.setPrice( carPrice ); c. cout << jaguar.getPrice( ); d. No! Because data member profit and member function getProfit( ) that returns the value of data member profit are private. e. hyunday = jaguar; hynday.setPrice( 24000.00 ); ©2011 Gilbert Ndjatou Page 271 Exercise C4 a. Demo1 addDemo1 ( Demo1 o1, Demo1 o2 ) { Demo1 temp; double res2; temp.val1 = o1.val1 + o2.val1; res2 = o1.getValue2( ) + o2.getValue2( ); temp.setValue2 ( res2 ); return ( temp ); } b. Demo1 obj1, obj2, objR; obj1.Val1 = 5; obj1.setValue2 ( 7 ); obj2.Val1 = 10; obj2.setValue2 ( 15 ); objR = addDemo1 ( obj1, obj2 ); Exercise C5 a. void updateDemo1 ( Demo1 & o ) { double num2; o.val1 += 10; num2 = o.getValue2 ( ); o.setValue2 ( num2 - 5 ); } b. Demo1 obj; obj.val1 = 15; obj.setValue2 ( 70 ); updateDemo1( obj ); Exercise O1 1. class OurClass { public: OurClass ( ); // default constructor OurClass ( int num, char symb); // constructor with parameters void setFirst(int newVal); // to set the value of data member first void setSecond(char newSymb); // to set the value of data member second int getFirst(void); // to return the value of data member first char getSecond( ); // to return the value of data member second void read(void); // to read the values of the two data members void print( ); // to output the values of the two data members private: int first; // the first data member char second; // the second data member }; ©2011 Gilbert Ndjatou Page 272 /*------------------------------Definition of the default constructor-----------------------------------*/ OurClass :: OurClass( ) { first = 0; second = „A‟; } /*------------------------------Definition of the constructor with parameters----------------------------*/ OurClass :: OurClass ( int num, char symb) { first = num; second = symb; } /*------------------------------member function setFirst( ) ----------------------------*/ void OurClass :: setFirst(int newVal) { first = newVal; } /*------------------------------member function setSecond( ) ----------------------------*/ void OurClass :: setSecond(char newSymb) { second = newSymb; } /*------------------------------member function getFirst( ) ----------------------------*/ int OurClass :: getFirst(void); { return first; } /*------------------------------member function getSecond( ) ----------------------------*/ int OurClass :: getSecond(void); { return second; } /*------------------------------member function read( ) ----------------------------*/ void OurClass :: read(void); { cin >> first >> second; } /*------------------------------member function print( ) ----------------------------*/ void OurClass :: print(void); { cout << endl << first << endl << second; } ©2011 Gilbert Ndjatou Page 273 2. /*------------------------------ function maxObj( ) ----------------------------*/ OurClass maxObj( OurClass obj1, OurClass obj2 ) { OurClass objR; int val1 = obj1.getFirst( ), val2 = obj2.getFirst( ); char symb1 = obj1.getSecond( ), symb2 = obj2.getSecond( ); if( val1 > val2 ) objR.setFirst( val1 ); else objR.setFirst( val2 ); if( symb1 > symb2 ) objR.setSecond( symb1 ); else objR.setSecond( symb2 ); return objR; } /*------------------------------ function incrObj( ) ----------------------------*/ void incrObj( OurClass & obj ) { int val = obj.getFirst( ); obj.setFirst( val + 1 ); } 3. OurClass objA, objB, objC( 100, „P‟ ); 4. a. objA.read( ); b. objB.setFirst( 15 ); c. int val = objC.getFirst( ); objC.setFirst ( val + 10 ); d. objC.print( ); e. OurClass newObj = maxObj( objA, objB ); f. incrObj( objC ); Exercise O3 a. MyClass obj1; b. MyClass obj2 ( 34, „A‟ ); c. MyClass obj3 ( ); Valid (but declaration of function obj3 ) d. MyClass obj4; obj4 = MyClass ( ); e. MyClass obj5; obj5 = MyClass ( 21, „Z‟); f. MyClass obj6 ( 10, „C‟ ); MyClass obj7 ( obj6 ); g. MyClass obj8 ( 5, „X‟ ); MyClass obj9 = obj8 ; h. MyClass obj10 = MyClass; Invalid ©2011 Gilbert Ndjatou Page 274 Exercise O5 class OurClass { public: OurClass ( int num = 0, char symb = „A‟); // constructor with parameters void setFirst(int newVal); // to set the value of data member first void setSecond(char newSymb); // to set the value of data member second int getFirst(void); // to return the value of data member first char getSecond( ); // to return the value of data member second void read(void); // to read the values of the two data members void print( ); // to output the values of the two data members private: int first; // the first data member char second; // the second data member }; /*------------------------------Definition of the constructor with parameters----------------------------*/ OurClass :: OurClass ( int num, char symb) : first( num ), second( symb ) { } Exercise O8 1. class Student { Public: Student( ); Student( string fname, string lname, int id, DayOfYear dbay, double g ); void read( void ); void print( ); private: string firtName; string lastName; int idNum; DayOfyear birthday; double gpa; }; 2. /*----------------------------default constructor ---------------------------------------------------*/ Student : : Student ( ) : idNum( 999999 ), gpa( 0 ) { } ©2011 Gilbert Ndjatou Page 275 /*------------------------------------------constructor with parameters ------------------------------------------------*/ Student : : Student( string fname, string lname, int id, DayOfYear dbay, double g ) : firstName( fname), lastName( lname ), birthday (bday ) { idNum = id; gpa = g; } /*---------------------------------- Member function read( ) --------------------------------------------------*/ void Student : : read( ) { cin >> firstName >> lastName >> idNum; birthDay.input( ); // read the values for the birth day month and day cin >> gpa; } /*---------------------------------- Member function print( ) --------------------------------------------------*/ void Student :: print( ) { cout << endl << “Name:\t” << lastName + “, “ + firstName; cout << endl << “ID NUM:\t” << idNum; cout << endl << “Birth Day:\t”; birthDay.output( ); // print the values for the birth day month and day cout << endl << “GPA:\t” << gpa; } 3. Student toto; // define object toto toto.read( ); // read values for the member variable of object toto toto.print( ); // output the values of the member variables of object toto 4. Student newStu ( “Mark”, “Depaul”, 1123, DayOfYear( 3, 25 ), 3.25 ); 5. newStu.print( ); Exercise O10 1. /*----------------------------default constructor ---------------------------------------------------*/ Item :: Item( ) { quantity = 0; } /*------------------------------------------constructor with parameters ------------------------------------------------*/ Item :: Item( string NewName, int newQtity ) : name( NewName), quantity( newQtity ) { } ©2011 Gilbert Ndjatou Page 276 /*---------------------------------- Member function read( ) --------------------------------------------------*/ void Item :: read( ) { cin >> name >> quantity; } /*---------------------------------- Member function setName( ) ----------------------------------------------*/ void Item :: setName( string newName ) { name = newName; } /*---------------------------------- Member function setQtity( ) -------------------------------------------------*/ void Item :: setQtity( int newQtity ) { quantity = newQtity; } /*---------------------------------- Member function getName( ) --------------------------------------------------*/ string Item :: getName( void ) { return ( name ); } /*---------------------------------- Member function getQtity( ) --------------------------------------------------*/ int Item :: getQtity( void ) { return ( quantity ); } /*---------------------------------- Member function print( ) --------------------------------------------------*/ void Item :: print( ) { cout << endl << “Name:\t” << name; cout << endl << “Quantity:\t” << quantity; } 2. class Item4Sale : public Item { public: Item4Sale( ); Item4Sale( string newName, int newQtity, double newUPrice ); double getUnitPrice( ); void setUnitPrice( double newUPrice ); void read( ); void print( ); private: double unitPrice; }; ©2011 Gilbert Ndjatou Page 277 3. Member Functions of class Item4Sale Access Specifiers Descriptions setName( ) public Set the new name of an item setQtity( ) public Set the new quantity of an item getName( ) public Return the name of an item getQtity( ) public Return the quantity of an item getUnitPrice( ) public Return the unit price of an item setUnitPrice( ) public Set the new unit price of an item Redefined function read( ) public Read the name, quantity, and unit price of an item Redefined function print( ) public Output the name, the quantity, and unit price of an item Data Member of class Item4Sale Access Specifiers name private Not accessible in a new/redefined member function quantity private Not accessible in a new/redefined member function unitPrice private Accessible in a new/redefined member function 4. /*----------------------------default constructor ---------------------------------------------------*/ Item4Sale :: Item4Sale( ) : Item( ), unitPrice( 1.00 ) { } /*------------------------------------------constructor with parameters ------------------------------------------------*/ Item4Sale :: Item4Sale( string NewName, int newQtity, double newUPrice ) : Item( NewName, newQtity) { unitPrice = newUPrice; } /*---------------------------------- Member function read( ) --------------------------------------------------*/ void Item4Sale :: read( ) { string iName; int iqtity; cin >> iname >> iqtity >> unitPrice; setName( iName ); setQtity( iqtity ); } /*---------------------------------- Member function print( ) --------------------------------------------------*/ void Item4Sale :: print( ) { cout << endl << “Name:\t” << getName( ); cout << endl << “Quantity:\t” << getQtity( ); cout << endl << Unit Price:\t” << unitPrice; } ©2011 Gilbert Ndjatou Page 278 /*---------------------------------- Member function setUnitPrice( ) -----------------------------------------*/ void Item4Sale :: setUnitPrice( double newUPrice ) { unitPrice = newUPrice; } /*---------------------------------- Member function getUnitPrice( )----------------------------------------*/ double Item4Sale :: getUnitPrice( ); { return (unitPrice) ; } 5. Output produced by: t1.print( ) Output produced by: t2.print( ) Name: Apple Quantity: 25 Name: Orange Quantity: 34 Unit Price: 0.20 Exercise O14 1. /*---------------------------------- Member function read( ) --------------------------------------------------*/ void Item4Sale :: read( ) { Item :: read( ); cin >> unitPrice; } /*---------------------------------- Member function print( ) --------------------------------------------------*/ void Item4Sale :: print( ) { Item :: print( ); cout << endl << Unit Price:\t” << unitPrice; } 2. a. Output produced by: t1.print( ) Output produced by: t2.print( ) Output produced by: t2.Item :: print( ) Name: Apple Quantity: 25 Name: Banana Quantity: 50 Unit Price: 0.10 Name: Banana Quantity: 50 b. t3.Item :: read( ); ©2011 Gilbert Ndjatou Page 279 Exercise O17 /*---------------------------------- Member function read( ) --------------------------------------------------*/ void Item4Sale :: read( ) { cin >> name >> quantity >> unitPrice; } /*---------------------------------- Member function print( ) --------------------------------------------------*/ void Item4Sale :: print( ) { cout << endl << “Name:\t” << Name; cout << endl << “Quantity:\t” << quantity; cout << endl << Unit Price:\t” << unitPrice; } Exercise O20 Statements: Output: t1.print( ); Name: Pie Quantity: 60 t3.print( ); Name: hat Quantity: 100 Unit Price: 30.00 helper ( t1 ); Name: Pie Quantity: 60 helper ( t3 ); Name: hat Quantity: 100 t2 = Item4Sale( “Shirt”, 150, 10.0 ); t2.print( ); Name: Shirt Quantity: 150 Exercise O22 Statements: Output: obj1.print( ); The price of the tile is: 2.00 obj2.print( ); The price of the tile is: 10.00 robj1.print( ); The length is: 0.5 The width is: 1.0 The price of the tile is: 1.00 robj2.print( ); The length is: 3.0 The width is: 5.0 The price of the tile is: 60.00 ©2011 Gilbert Ndjatou Page 280