using System;

public class Program

{

    public static void Main()

    {

        int a;

        var obj  = new Source();

        Console.WriteLine("Sum={0}",obj.Add(10,20));

        var msg = "Result";

        Console.WriteLine("Second method:{0}",obj.Add(10,20,msg));

        Console.WriteLine("Out method: {0}",obj.Add(a));

    }

}

​

​

public class Source

{

public int Add(int a, int b)

{

return a+b;

}

​

public string Add(int a, int b, string msg)

{

int s = a+ b;

    var str = string.Format("{0} {1} + {2} = {3}",msg,a,b,s);

return str;

}

​

public static void Add(out int a)

{

 a = 30 + 3;

//return a

}

}

​