#include <ctype.h>

int toupper(int c);

#include <ctype.h>
main(){
 char s[] = "aBcDeFgH12345;!#$";
 int i;
 printf("before toupper() : %s\n", s);
 for(i = 0; i < sizeof(s); i++)
  s[i] = toupper(s[i]);
 printf("after toupper() : %s\n", s);
}

before toupper() : aBcDeFgH12345;!#$
after toupper() : ABCDEFGH12345;!#$

#include <stdlib.h>

int tolower(int c);

#include <ctype.h>
main(){
 char s[] = "aBcDeFgH12345;!#$";
 int i;
 printf("before tolower() : %s\n", s);
 for(i = 0; i < sizeof(s); i++)
  s[i] = tolower(s[i]);
 printf("after tolower() : %s\n", s);
}

before tolower() : aBcDeFgH12345;!#$
after tolower() : abcdefgh12345;!#$