/* vim: set tabstop=4 shiftwidth=4 fileencoding=utf-8 noexpandtab: */
#include <stdio.h>
#include <stdlib.h>
void transform_string(/* TODO */) {  // works IN PLACE, i.e., modifies string
    for(int i=0; i < strlen(s); i++) {
        s[i] = /* TODO */
    }
}
char to_lower(char ch) {
    if(ch >= 'A' && ch <= 'Z') {
        return 'a' + ch - 'A';
    }
    else {
        return ch;
    }
}
char to_upper(char ch) {
    return ((ch >= 'a' && ch <= 'z') ? ('A' + ch - 'a') : ch);
}
int main(int argc, char* argv[]) {
    char s[] = "happy";
    transform_string(s, to_upper);
    printf("%s", s); // print "HAPPY"
    return EXIT_SUCCESS;
}