The tolower function converts c to a lowercase character. If c is not an alphabetic letter, the tolower function has no effect.

The tolower function returns the lowercase equivalent of c.

_tolower, _toupper, toupper

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

void tst_tolower (void) {
  unsigned char i;

  for (i = 0x20; i < 0x7F; i++) {
    printf ("tolower(%c) = %c\n", i, tolower(i));
  }
}