Getting information about characters

The next thing we might want to do to individual characters has to do with figuring out what kind of character it is. Given a character from an input source, we may want to determine one or more of the following properties of that character:

• Is it a control character?
• Is it whitespace? (that is, does it include SPACE, TAB, LF, CR, VT, or HT?)
• Is it a digit or a letter?
• Is it in uppercase or not?
• Is it even ASCII?

Now, reflecting on the four groups of ASCII characters and how they are laid out, you might consider how you would write functions to test these properties. For instance, to see whether a character is a decimal digit, you could write the following:

bool isDigit( int c )  {
  bool bDigit = false;
  if( c >= '0' && c <= '9' ) 
    bDigit = true;
  return bDigit;
}

This function checks to see whether the value of the...