isalpha() - alphabetic character test
#include <ctype.h>
int isalpha (int c)
In the POSIX/C locale, the isalpha(3) function tests for any character for which isupper(3) or islower(3) is true. More generally, it tests for any character for which none of iscntrl(3), isdigit(3), ispunct(3), or isspace(3) is true.
The isalpha(3) function returns zero if the character tests false and returns non-zero if the character tests true.
isalnum(3)
isblank(3)
iscntrl(3)
isdigit(3)
isgraph(3)
islower(3)
isprint(3)
ispunct(3)
isspace(3)
isupper(3)
isxdigit(3)
tolower(3)
toupper(3)