The toupper function converts c to an uppercase character. If c is not an alphabetic letter, the toupper function has no effect.

The toupper function returns the uppercase equivalent of c.

_tolower, _toupper, tolower

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

void tst_toupper (void) {
  unsigned char i;

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