#include <ctype.h>int isblank(int ch);
The isblank( ) function was added by C99.
The isblank( ) function returns nonzero if ch is a character for which isspace( ) returns true and is used to separate words. Thus, for English, the blank characters are space and horizontal tab.
Related functions are isalnum( ), isalpha( ), iscntrl( ), isdigit( ), isgraph( ), ispunct( ), and isspace( ).