Getting number of days in a month

I have a comboBox with all of the months in it.

What I need to know is the number of days in the chosen month.

var month = cmbMonth.SelectedIndex + 1;
DateTime date = Convert.ToDateTime(month);

So if a user selects January, I need to save 31 to a variable.

You want DateTime.DaysInMonth:

int days = DateTime.DaysInMonth(year, month);

Obviously it varies by year, as sometimes February has 28 days and sometimes 29. You could always pick a particular year (leap or not) if you want to "fix" it to one value or other.

Use System.DateTime.DaysInMonth, from code sample:

const int July = 7;
const int Feb = 2;

// daysInJuly gets 31.
int daysInJuly = System.DateTime.DaysInMonth(2001, July);

// daysInFeb gets 28 because the year 1998 was not a leap year.
int daysInFeb = System.DateTime.DaysInMonth(1998, Feb);

// daysInFebLeap gets 29 because the year 1996 was a leap year.
int daysInFebLeap = System.DateTime.DaysInMonth(1996, Feb);

To find the number of days in a month, DateTime class provides a method "DaysInMonth(int year, int month)". This method returns the total number of days in a specified month.

public int TotalNumberOfDaysInMonth(int year, int month)
    {
        return DateTime.DaysInMonth(year, month);
    }

OR

int days = DateTime.DaysInMonth(2018,05);

Output :- 31

  int month = Convert.ToInt32(ddlMonth.SelectedValue);/*Store month Value From page*/
  int year = Convert.ToInt32(txtYear.Value);/*Store Year Value From page*/
  int days = System.DateTime.DaysInMonth(year, month); /*this will store no. of days for month, year that we store*/

 int days = DateTime.DaysInMonth(int year,int month);

or

 int days=System.Globalization.CultureInfo.CurrentCulture.Calendar.GetDaysInMonth(int year,int month);

you have to pass year and month as int then days in month will be return on currespoting year and month

I made it calculate days in month from datetimepicker selected month and year , and I but the code in datetimepicker1 textchanged to return the result in a textbox with this code

private void DateTimePicker1_ValueChanged(object sender, EventArgs e)
{
    int s = System.DateTime.DaysInMonth(DateTimePicker1.Value.Date.Year, DateTimePicker1.Value.Date.Month);

    TextBox1.Text = s.ToString();
} 

int days = DateTime.DaysInMonth(DateTime.Now.Year, DateTime.Now.Month);

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if you want to find days in this year and present month then this is best