C# DateTime operator +=

I have two variables in type of DateTime, and I want to sum them, how can I do it开发者_StackOverflow中文版? I get compilation error that says DateTime dosen't have operator +=

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You cannot add two DateTime values together. It wouldn't have any meaning. A DateTime represents a single point in time, whereas a TimeSpan represents a duration. Adding a point in time to a duration results in another point in time. You can only add TimeSpan values to DateTime values–and it does support += in that case:

dateTime += timeSpan;

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Just to answer the comment in Mehrdad's answer - yes, it looks like those should both be regarded as TimeSpans instead of DateTime values... and yes, you can add time spans together too.

If you're using .NET 4, you can use a custom format string to parse the first part of the lines, e.g. "00:00:01.2187500".

Sample code:

using System;
using System.Globalization;

public class Test
{
    static void Main()
    {
        string line1 = "00:00:01.2187500 CA_3";
        string line2 = "00:00:01.5468750 CWAC_1";

        TimeSpan sum = ParseLine(line1) + ParseLine(line2);
        Console.WriteLine(sum);
    }

    static TimeSpan ParseLine(string line)
    {
        int spaceIndex = line.IndexOf(' ');
        if (spaceIndex != -1)
        {
            line = line.Substring(0, spaceIndex);
        }
        return TimeSpan.ParseExact(line, "hh':'mm':'ss'.'fffffff",
                                   CultureInfo.InvariantCulture);
    }
}

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You can use the DateTime.ToOADate Method :

DateTime D1 = DateTime.Today;
DateTime D2 = DateTime.Today.AddMonths(2);

double days = D1.ToOADate() + D2.ToOADate();