#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>

int *toUpper(char *str){
    if (str) {
       if (str[0] != '\0'){     // check the first element
            int i;
            for (i = 0; i < strlen(str); i++) {
            if (str[i] >= 'a' && str[i] <= 'z') {
            str[i] = str[i] - 'a' + 'A';
                }
            }
       }
       return str;
     }
     else{ // else
            printf("rossz");
     return NULL;      //indicate error condition
     }
 }

int main(int argc, char **argv)
{
     for (int i = 1; i < argc; ++i)
    {
        printf(toUpper(argv[i]));
    }
}