isalpha

The isalpha function tests c to determine if it is an alphabetic character ('A'-'Z' or 'a'-'z').

The isalpha function returns a value of 1 if c is an alphabetic character or a value of 0 if it is not.

isalnum, iscntrl, isdigit, isgraph, islower, isprint, ispunct, isspace, isupper, isxdigit

#include <ctype.h>
#include <stdio.h> /* for printf */

void tst_isalpha (void) {
  unsigned char i;
  char *p;

  for (i = 0; i < 128; i++) {
    p = (isalpha (i) ? "YES" : "NO");

    printf ("isalpha (%c) %s\n", i, p);
  }
}