Write a C++ program that repeatedly reads lines until an EOF is encountered. As each line is read, the program strips out all characters that are not upper or lower case letters or spaces, and then outputs the line. Thus, the program acts as a filter and issues no prompt. There are many ways this program could be written, but to receive full credit, you must observe the following:

Place your code in a file called filterChars.cpp.

The program should consist of four functions whose prototypes are:
- int main(); o void removeNonAlpha(string& str);
- bool isUpperCaseLetter(char ch);
- bool isLowerCaseLetter(char ch);

The main() function should

1. read string input - an entire line, including spaces (try getline())
2. call removeNonAlpha() to process the input string
3. print out the string as altered by removeNonAlpha()
4. not call isUpperCaseLetter() or isLowerCaseLetter() directly

The function removeNonAlpha() alters its string reference variable by removing all characters that aren't upper or lower case letters or spaces. Use the function erase() in the string class to remove the characters. Use the functions isUpperCaseLetter() and isLowerCaseLetter() to help identify which characters to remove.

The functions isUpperCaseLetter() and isLowerCaseLetter() simply return true if the character parameter is an upper-case or lower-case letter, respectively, and false otherwise. These two functions can easily be one-liners. Note: DonA????1t use any library functions (specifically, use neither islower nor isupper) in isUpperCaseLetter() and isLowerCaseLetter(). Use an if statement instead.

Use
   while(getline(cin, inString)).
for the input.