Solution: Fix the Code

import std.stdio;
import std.string;
import std.exception;
/* Reads the time as hour and minute after printing a
 * message. */
void readTime(string message,
              out int hour,
              out int minute) {
    write(message, "? (HH:MM) ");
    readf(" %s:%s", &hour, &minute);
    enforce((hour >= 0) && (hour <= 23) &&
            (minute >= 0) && (minute <= 59),
            "Invalid time!");
}
/* Returns the time in string format. */
string timeToString(int hour, int minute) {
    assert((hour >= 0) && (hour <= 23));
    assert((minute >= 0) && (minute <= 59));
    return format("%02s:%02s", hour, minute);
}
/* Adds duration to start time and returns the result as the
 * third pair of parameters. */
void addDuration(int startHour, int startMinute,
                 int durationHour, int durationMinute,
                 out int resultHour, out int resultMinute) {
    resultHour = startHour + durationHour;
    resultMinute = startMinute + durationMinute;
    resultHour += resultMinute / 60; resultHour %= 24;
    resultMinute %= 60;
    assert((resultHour >= 0) && (resultHour <= 23));
    assert((resultMinute >= 0) && (resultMinute <= 59));
}
void main() {
    int startHour;
    int startMinute;
    readTime("Start time", startHour, startMinute);
    int durationHour;
    int durationMinute;
    readTime("Duration", durationHour, durationMinute);
    int endHour;
    int endMinute;
    addDuration(startHour, startMinute,
                durationHour, durationMinute,
                endHour, endMinute);
    writefln("%s hours and %s minutes after %s is %s.",
             durationHour, durationMinute,
             timeToString(startHour, startMinute),
             timeToString(endHour, endMinute));
}