3. Character classification functions

• When using character input, you often need one or more of character classification routines from <cctype> header:

  
      isspace(c);    // is c whitespace? (' ', '\t', '\n', etc.)
      isalpha(c);    // is c a letter? ('a'..'z', 'A'..'Z') note: not '_'
      isdigit(c);    // is c a decimal digit? ('0'..'9')
      isxdigit(c);   // is c hexadecimal digit: decimal digit or 'a'..'f' or 'A'..'F'
      isupper(c);    // is c an upper-case letter?
      islower(c);    // is c a lower-case letter?
      isalnum(c);    // is c a letter or a decimal digit?
      iscntrl(c);    // is c a control character (ACSII 0..31 and 127)
      ispunct(c);    // is c not a letter, digit, whitespace, or invisible control character
      isprint(c);    // is c printable (ASCIII ' '..'~')
      isgraph(c);    // is c isalpha()|isdigit()|ispunct() (note, not space)
  
      toupper(c);    // c or c's upper case equivalent
      tolower(c);    // c or c's lower case equivalent