C Programming on the IBM PC (C Programmers Reference Guide Series)

isalnum

#include <ctype.h>int isalnum(int ch);

The isalnum( ) function returns nonzero if its argument is either a letter of the alphabet or a digit. If the character is not alphanumeric, zero is returned.

Related functions are isalpha( ), iscntrl( ), isdigit( ), isgraph( ), isprint( ), ispunct( ), and isspace( ).