WTF time is it in UTC

wtft.c

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <memory.h>

void display_current_time(const char *name, short tz){
    time_t t;
    struct tm *tdata;
    time(&t);
    tdata = gmtime(&t);
    printf("\t%s:\t%2d:%02d\n", name, (tdata->tm_hour + tz) % 24, tdata->tm_min);
}

void display_time_for_utc(const char *name, short utc_hour, short tz){
    short tz_time;
    tz_time = utc_hour + tz;
    if (tz_time < 0){
        tz_time = 24 + tz_time;
        printf("%s: %2d:%02d the previous day when it is: %2d:%02d UTC\n",
               name, tz_time, 0, utc_hour, 0);
    } else if (tz_time > 24){
        tz_time %= 24;
        printf("%s: %2d:%02d the next day when it is: %2d:%02d UTC\n",
               name, tz_time, 0, utc_hour, 0);
    } else {
        printf("%s: %2d:%02d when it is %2d:%02d UTC\n",
               name, tz_time, 0, utc_hour, 0);
    }
}

int main(int argc, char *argv[]){

    int i;
    short utc_hour;
    char *end;
    for (i = 1; i < argc; ++i){
        utc_hour = strtol(argv[i], &end, 10);
        if (end != argv[i]+strlen(argv[i])){
            printf("Expected UTC hour as argument. Not '%s'\n", argv[i]);
        } else {
            if (utc_hour > 24){
                printf("Converting %d to %d (24 hour time)\n", utc_hour, utc_hour % 24);
                utc_hour %= 24;
            }
            display_time_for_utc("PST", utc_hour, (-8));
            display_time_for_utc("AEST", utc_hour, (+10));
        }
    }
    printf("Current time:\n");
    display_current_time("UTC", 0);
    display_current_time("PST", (-8));
    display_current_time("AEST", (+10));
    return 0;

}