using System;

public class A{
  private int a, b, c;
  private int r;

  public A(){
    a = 1; b = 2; c = 3;
  }

  public void DoAdd(int v1, int v2, int v3, out int v){  
    v = v1 + v2 + v3;                                    
  }
 
  public override string ToString(){
    return String.Format("{0} {1} {2}. {3}", a, b, c, r);
  }

  public void Go(){
    Console.WriteLine("{0}", this);
    DoAdd(a, b, c, out r);   
    Console.WriteLine("{0}", this);
  }    

  public static void Main(){
    new A().Go();
  }
}

 
 
 
 
 
 
 
 
 
 
v is an out parameter. It is used as
an alternative to return v1 + v2 + v3. 
 
 
 
 
 
 
 
 
The keyword out is also used on the actual parameter!