Get last/next week Wednesday date in C#

Question

How would I get last week Wednesday and next week Wednesday\'s date in C#:

public Form1()
{
   InitializeComponent();
   CurrentDate.Text = \"Today\'s Date: \" +         


        

Answer 1

One of the problems with some of the answers is that the DayoyOfWeek is an enum with values 0-6. When a subsequent day of week equates to Sunday (enum value = 0), but you gave a Tuesday (enum value=2), and you want next tuesday, the calculation goes wrong if you just peform a calculation.

The class with two methods which I cam up with for my own use on a project I am working on is.

public static class DateHelper
{
    public static DateTime GetDateForLastDayOfWeek(DayOfWeek DOW, DateTime DATE)
    {
        int adjustment = ((int)DATE.DayOfWeek < (int)DOW ? 7 : 0);
        return DATE.AddDays(0- (((int)(DATE.DayOfWeek) + adjustment) - (int)DOW));
    }

    public static DateTime GetDateForNextDayOfWeek(DayOfWeek DOW, DateTime DATE)
    {
        int adjustment = ((int)DATE.DayOfWeek < (int)DOW ? 0 : 7);
        return DATE.AddDays(((int)DOW) - ((int)(DATE.DayOfWeek)) + adjustment);
    }
}

The XUnit tests proving the code above works.

public class DateHelperUnitTests
{

    [Theory]
    [InlineData(2020, 1, 7, 2020, 1, 7)]
    [InlineData(2020, 1, 8,  2020, 1, 7)]
    [InlineData(2020, 1, 9,  2020, 1, 7)]
    [InlineData(2020, 1, 10, 2020, 1, 7)]
    [InlineData(2020, 1, 11, 2020, 1, 7)]
    [InlineData(2020, 1, 12, 2020, 1, 7)]
    [InlineData(2020, 1, 13, 2020, 1, 7)]
    [InlineData(2020, 1, 14, 2020, 1, 14)]
    [InlineData(2020, 1, 15, 2020, 1, 14)]
    public void GetDateForLastDayOfWeek_MultipleValues_Pass(
        int InputYear, int InputMonth, int InputDay,
        int ExpectedYear, int ExpectedMonth, int ExpectedDay)
    {
        DateTime DateToTest = new DateTime(InputYear, InputMonth, InputDay);
        DateTime NewDate = DateHelper.GetDateForLastDayOfWeek(DayOfWeek.Tuesday, DateToTest);
        DateTime DateExpected = new DateTime(ExpectedYear,ExpectedMonth,ExpectedDay);

        Assert.True(0 == DateTime.Compare(DateExpected.Date, NewDate.Date));
    }

    [Theory]
    [InlineData(2020, 1, 7, 2020, 1, 14)]
    [InlineData(2020, 1, 8, 2020, 1, 14)]
    [InlineData(2020, 1, 9, 2020, 1, 14)]
    [InlineData(2020, 1, 10, 2020, 1, 14)]
    [InlineData(2020, 1, 11, 2020, 1, 14)]
    [InlineData(2020, 1, 12, 2020, 1, 14)]
    [InlineData(2020, 1, 13, 2020, 1, 14)]
    [InlineData(2020, 1, 14, 2020, 1, 21)]
    [InlineData(2020, 1, 15, 2020, 1, 21)]
    public void GetDateForNextDayOfWeek_MultipleValues_Pass(
        int InputYear, int InputMonth, int InputDay,
        int ExpectedYear, int ExpectedMonth, int ExpectedDay)
    {
        DateTime DateToTest = new DateTime(InputYear, InputMonth, InputDay);
        DateTime NewDate = DateHelper.GetDateForNextDayOfWeek(DayOfWeek.Tuesday, DateToTest);
        DateTime DateExpected = new DateTime(ExpectedYear, ExpectedMonth, ExpectedDay);

        Assert.True(0 == DateTime.Compare(DateExpected.Date, NewDate.Date));
    }
}