public string add()
{
 return "hello";
}

public string add(string a)
{
 return a;
}

public string add(string a, string b)
{
 return a+b;
}

protected void Button1_Click(object sender, EventArgs e)
    {
        Response.Write("<br />" + AddNumbers().ToString());
        Response.Write("<br />" + AddNumbers(1, 2).ToString());
        Response.Write("<br />" + AddNumbers(1, 2, 3).ToString());
    }

    public int AddNumbers()
    {
        return 0;
    }

    public int AddNumbers(int FirstNumber, int SecondNumber)
    {
        return FirstNumber + SecondNumber;
    }

    public int AddNumbers(int FirstNumber, int SecondNumber, int ThirdNumber)
    {
        return FirstNumber + SecondNumber + ThirdNumber;
    }

Private void Testing(int i=0,string name)
{
  //Implement the code
}

Testing("Name1");
Testing(1,"Name2");

protected void Page_Load(object sender, EventArgs e)
    {
        Response.Write("<br />" + AddNumbers(1, 2, 3));
        Response.Write("<br />" + AddNumbers(5, 6));
        Response.Write("<br />" + AddNumbers());
    }

    public int AddNumbers(params int[] numbers)
    {
        int total = 0;
        foreach (int num in numbers)
        {
            total += num;
        }
        return total;
    }

//Optional parameter using C# 4.0
public int Add(int Number1, int Number2, int Number3 = 0)
{
return Number1 + Number2 + Number3;
}