Calculate DateTime for upcoming day of week

Question

This is the code I have at the moment:

String getDayRequested;
public void setDay(String getDayFromForm1)
{
   getDayRequested = getDayFromForm1;
   {
      if (getDayRequested.Contains("today"))
      {
         getDayRequested = DateTime.Today.DayOfWeek.ToString();
      }
      else if (getDayRequested.Contains("tomorrow"))
      {
         getDayRequested = DateTime.Today.AddDays(1).DayOfWeek.ToString();
   }
}

This checks my TextBox.Text string from Form1, and checks to see if the text "today" or "tomorrow" is in it.

Can anyone help me in the right direction of how to check the string for information asked about upcoming days; ie: "What will be the date this saturday", and add the appropriate number of days depending on what the day is when asked.

UPDATE

Using the code in the accepted answer, I used the following in my above else if statement to complete what I was after:

else if (getDayRequested.Contains("monday"))
{
   getDayRequested = GetFutureDay(DateTime.Now, DayOfWeek.Monday).ToString("dd");
}

Answer 1

This handy little method will return a future day of the week.

public DateTime GetFutureDay(DateTime start, DayOfWeek day)
{
    int daysToAdd = (day - start.DayOfWeek + 7) % 7;
    return start.AddDays(daysToAdd);
}

It would be called like:

var day = (DayOfWeek)Enum.Parse(typeof(DayOfWeek), getDayFromForm1);
var getDayRequested = GetFutureDay(DateTime.Now, day);

Answer 2

Consider the following snippet of code...

DateTime date;
public void setDay(String day)
{
    DayOfWeek futureDay = (DayOfWeek)Enum.Parse(typeof(DayOfWeek), day);
    int futureDayValue = (int)futureDay;
    int currentDayValue = (int)DateTime.Now.DayOfWeek;
    int dayDiff = futureDayValue - currentDayValue;
    if (dayDiff > 0)
    {
        date = DateTime.Now.AddDays(dayDiff);
    }
    else
    {
        date = DateTime.Now.AddDays(dayDiff + 7);
    }


}

Good Luck!