isdigit

iscntrl

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

The iscntrl( ) function returns nonzero if ch is a control character, which in ASCII environments is a value between zero and 0x1F, or equal to 0x7F (DEL). Otherwise, zero is returned.

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