| Function | A non-zero (true) value is returned if... |
|---|---|
| int isalpha( char ) | c is a letter |
| int isupper( char ) | c is an uppercase letter |
| int islower( char ) | c is a lowercase letter |
| int isdigit( char ) | c is a digit |
| int isalnum( char ) | c is a letter or digit |
| int isxdigit( char) | c is a hex digit |
| int isspace( char ) | c is a whitespace character |
| int ispunct( char ) | c is a punctuation character |
| int isprint( char ) | c is a printable character |
| int isgraph( char) | c printable, not space |
| int iscntrl( char ) | c is a control character |
| int isascii( char ) | c is an ASCII code |