Returns nonzero when c is either a character or a number
int isalnum( int c )
Returns nonzero when c is an alphanumerical character
int isalpha( int c )
Returns nonzero when c is a blank (either space or tab)
int isblank( int c )
Returns nonzero when c is a control character
int iscntrl( int c )
Returns nonzero when c is a decimal digit (number)
int isdigit( int c )
Returns nonzero when c is printable character, excluding space
int isgraph( int c )
Returns nonzero when c is an lowercase character
int islower( int c )
Returns nonzero when c is printable character, including space
int isprint( int c )
Returns nonzero when c is a punctuation character (c is not a control, space, letter or number)
int ispunct( int c )
Returns nonzero when c is a whitespace character
int isspace( int c )
Returns nonzero when c is an uppercase character
int isupper( int c )
Returns nonzero when c is an hexadecimal digit
int isxdigit( int c )
Returns the lowercase version of a character
int tolower( int c )
Returns the uppercase version of a character
int toupper( int c )