What is the easiest way to subtract time in C#?

Question

I'm trying to put together a tool that will help me make work schedules. What is the easiest way to solve the following?

• 8:00am + 5 hours = 1:00pm
• 5:00pm - 2 hours = 3:00pm
• 5:30pm - :45 = 4:45

and so on.

Chanteuse

Answer 1

These can all be done with DateTime.Add(TimeSpan) since it supports positive and negative timespans.

DateTime original = new DateTime(year, month, day, 8, 0, 0);
DateTime updated = original.Add(new TimeSpan(5,0,0));

DateTime original = new DateTime(year, month, day, 17, 0, 0);
DateTime updated = original.Add(new TimeSpan(-2,0,0));

DateTime original = new DateTime(year, month, day, 17, 30, 0);
DateTime updated = original.Add(new TimeSpan(0,-45,0));

Or you can also use the DateTime.Subtract(TimeSpan) method analogously.

Isadoraisadore

ok so where did i go wrong. i added a datetimepicker and assigned its value to a datetime variable. now the math methods aren't showing up – Chanteuse

@Chanteuse - probably worth posting some code, this is a slightly different question than date-time arithmetic – Isadoraisadore

@Chanteuse When you use a DateTimePicker, bear in mind it can show either date or time-of-day, but maintains a Value composed of both... if you're using the Value property you may need to subtract one or the other component first. – Knowledge

In the third example the OP wants to subtract 45 minutes, why in this answer I don't see a negative value? Is this a mistake? – Gust

Answer 2

Check out all the DateTime methods here: http://msdn.microsoft.com/en-us/library/system.datetime.aspx

Add Returns a new DateTime that adds the value of the specified TimeSpan to the value of this instance.

AddDays Returns a new DateTime that adds the specified number of days to the value of this instance.

AddHours Returns a new DateTime that adds the specified number of hours to the value of this instance.

AddMilliseconds Returns a new DateTime that adds the specified number of milliseconds to the value of this instance.

AddMinutes Returns a new DateTime that adds the specified number of minutes to the value of this instance.

AddMonths Returns a new DateTime that adds the specified number of months to the value of this instance.

AddSeconds Returns a new DateTime that adds the specified number of seconds to the value of this instance.

AddTicks Returns a new DateTime that adds the specified number of ticks to the value of this instance.

AddYears Returns a new DateTime that adds the specified number of years to the value of this instance.

Swage

For everyone that comes over this: You can use these functions above and use a negative value to subtract, as long as the instance hasn't been initialised to DateTime.MinValue – Dorsad

Answer 3

Hi if you are going to subtract only Integer value from DateTime then you have to write code like this

DateTime.Now.AddHours(-2)

Here I am subtracting 2 hours from the current date and time

Northwester

Answer 4

This works too:

System.DateTime dTime = DateTime.Now();

// tSpan is 0 days, 1 hours, 30 minutes and 0 second.
System.TimeSpan tSpan = new System.TimeSpan(0, 1, 3, 0); 

System.DateTime result = dTime + tSpan;

To subtract a year:

DateTime DateEnd = DateTime.Now;
DateTime DateStart = DateEnd - new TimeSpan(365, 0, 0, 0);

Hixon

Answer 5

Use the TimeSpan object to capture your initial time element and use the methods such as AddHours or AddMinutes. To substract 3 hours, you will do AddHours(-3). To substract 45 mins, you will do AddMinutes(-45)

Hardworking

Use the TimeSpan object to capture your initial time element - do you mean DateTime? – Tartan

I am referring to System.TimeSpan type – Hardworking

But the initial time is an instant e.g. 8:00pm rather than a time span e.g. 45 minutes. (Also apologies, I just realised how old a post this is.) – Tartan

But that's what I meant. You will write ts = new TimeSpan(8, 0, 0) for 8am or ts = new Timespan(20, 0, 0) for 8pm, then you will do ts.AddMinutes(45) – Hardworking

Eh... I suppose that works OK if you genuinely don't care about the date, but that's semantically not what a timespan represents, and it would really boost your WTFpm rating. – Tartan

Not disagreeing with your comment :) Like you said, been a long while last I answered this post. At that time, it was a spontaneous response to answer the question specifically just on performing simple operation on time. – Hardworking

Yeah, I know exactly what you mean there. I won't pretend some of my old answers wouldn't provide a few WTFs themselves :) – Tartan

Answer 6

try this

namespace dateandtime
{

    class DatesTime
    {

        public static DateTime Substract(DateTime now, int hours,int minutes,int seconds)
        {
            TimeSpan T1 = new TimeSpan(hours, minutes, seconds);
            return now.Subtract(T1);
        }


        static void Main(string[] args)
        {
            Console.WriteLine(Substract(DateTime.Now, 36, 0, 0).ToString());

        }
    }
}

Vaporization

Answer 7

DateTime original = new DateTime(year, month, day, 8, 0, 0); DateTime updated = original.Add(new TimeSpan(5,0,0));

DateTime original = new DateTime(year, month, day, 17, 0, 0); DateTime updated = original.Add(new TimeSpan(-2,0,0));

DateTime original = new DateTime(year, month, day, 17, 30, 0); DateTime updated = original.Add(new TimeSpan(0,-45,0));

Killen

Answer 8

TimeLeftToOpen= new TimeSpan(TimeLeftToOpen.Hours, TimeLeftToOpen.Minutes, TimeLeftToOpen.Seconds - 1);

Bedford

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