The Output Parameters

Sometimes when you write a function, you may want it to manipulate and return several values rather than one. Whenever I needed to do this I used to return an object.
But there might be a possibility that the returned object has no other purpose than to be used just to return multiple values from a function.
And then I discovered output parameters. Though I haven't really used them. (Just used them to check the functionality, nothing flashy. :) )

With output parameters you define the variables that will be returned. But you don't use the return keyword. With return keyword you can return a single value or object not multiple.
But with output parameters you don't use the return keyword to return multiple values rather you just specify that these variables are output parameters and their values can be used by the calling program and the called program can manipulate their values (in fact, assign them values).
For the above stated purposes you use the keyword out.

Example Code:
Say, you have a class "Class1.cs" (a very innovative name, right?)
In this class you have a function called ProcessNum which takes two integers as input and as output gives their sum and difference. This is how it will work:

public void ProcessNum(int a, int b, out int Sum, out int Diff)
{
Sum = a + b;
Diff = a - b;
}

Calling ProcessNum:

Class1 obj = new Class1();
int S;
int D;
int num1 = 5;
int num2 = 5;
obj.ProcessNum(num1, num2, out S, out D);
Console.WriteLine("Called ProcessNum of Class1 with parameters " +
"a: " + num1 + Environment.NewLine + " b: " + num2 +
Environment.NewLine + "Returned Values:::: " +
Environment.NewLine + "Sum: " + S + Environment.NewLine +
"Diff: " + D);

Source:

Apress Beginning ASP.Net 2.0 in C# 2005
Chapter # 3: Types, Objects and Namespaces
Pg. #: 75