int string_length(char *s) {
    return strlen(s);
}

char* string_upper(char *s) {
    return upper(s);
}

char* string_lower(char *s) {
    return lower(s);
}

int string_contains(char *haystack, char *needle) {
    int pos = strpos(haystack, needle);
    if (pos >= 0) {
        return 1;
    }
    return 0;
}