You can get the total days in a month easily by giving year and month as inputs.
Year is mandatory here because C# has to validate like leap year functionality internally.
(i.e) 2011 - 02 --> 28 days
2012 -02 --> 29 days.

Syntax:

DaysInMonth(int year, int month)

Example:

using System;
 
namespace forgetCode
{
    class Program
    {
        static void Main(string[] args)
        {
        
     Console.WriteLine("Enter year");
     int year = Convert.ToInt32(Console.ReadLine());
 
 
     Console.WriteLine("Enter month");
     int month = Convert.ToInt32(Console.ReadLine());
 
            
     Console.WriteLine("Days in the month:"+DateTime.DaysInMonth(year,month));                    
        }
 
    }
}

Output:

Enter year
2012
Enter month
02
Days in the month :29


Enter year
2015
Enter month
02
Days in the month :28


..