Question

Trying to emulate the rollover of a 24 hour clock by hand (with math vs. using the timespan classes). The incrementing part was easy to figure out how to roll over from 23:00 to 0:00 and from, but getting it to go the other way is turning out to be really confusing. Here’s what I have so far:

static void IncrementMinute(int min, int incr)
{
    int newMin = min + incr,
                hourIncrement = newMin / 60;

    //increment or decrement the hour
    if((double)newMin % 60 < 0 && (double)newMin % 60 > -1)
        hourIncrement = -1;

    Console.WriteLine("Hour increment is {0}: ", hourIncrement);
}

The problem that im finding is when going backwards, if the the modulus of is between numbers, it will not decrement correctly. Example: it is 12:00 and you subtract 61 minutes, we know the time would be 10:59 as the hour should roll back 1 hour for going from 12:00 to 11:59, then back again for going from 11:00 to 10:59. Unfortunately the way im calculating it: newMin % 60 in this case, only grabs the first hour rollback, but since the second rollback is technically -1.0166 as a remainder, and since mod only returns a whole number, its rounding off. Im sure im missing some basic math here, but could someone help me out?

EDIT: I’ve written this a number of ways long and short. Some are closer than others, but I know this is simpler than it seems. I know this one seems kinda “wtf was he doing”, but you should be able to see basically what Im trying to do. Incrementing a clock and having it rollover from 23:59 to 0:00 is easy. Going backwards has proven to be not so easy.

OK, here’s the incrementMinute with the rollover. Simple. But try to go backwards. Doesn’t work.

static void IncrementMinute(int min, int incr)

        {
            int newMin = min + incr,
                hourIncrement = newMin / 60;

            min = newMin % 60;

            Console.WriteLine("The new minute is {0} and the hour has incremented by {1}", min, hourIncrement);
        }

Answer 1

I’d go for something a bit simpler

public class Clock
{
    public const int HourPerDay = 24;
    public const int MinutesPerHour = 60;
    public const int MinutesPerDay = MinutesPerHour * HourPerDay;

    private int totalMinutes;

    public int Minute
    {
        get { return this.totalMinutes % MinutesPerHour; }
    }

    public int Hour
    {
        get { return this.totalMinutes / MinutesPerHour; }
    }

    public void AddMinutes(int minutes)
    {
        this.totalMinutes += minutes;
        this.totalMinutes %= MinutesPerDay;
        if (this.totalMinutes < 0)
            this.totalMinutes += MinutesPerDay;
    }

    public void AddHours(int hours)
    {
        this.AddMinutes(hours * MinutesPerHour);
    }

    public override string ToString()
    {
        return string.Format("{0:00}:{1:00}", this.Hour, this.Minute);
    }
}

Sample usage :

new Clock().AddMinutes(-1);    // 23:59
new Clock().AddMinutes(-61);   // 22:59
new Clock().AddMinutes(-1441); // 23:59
new Clock().AddMinutes(1);     // 00:01
new Clock().AddMinutes(61);    // 01:01
new Clock().AddMinutes(1441);  // 00:01