# Design Patterns(C#): Basic example Strategy pattern

In this example I´m going to explane the strategy pattern. With this example you can do a calculation with two numbers (-/+) and expand the number of operators (/, *, etc.).

First create a interface which defines the interface of the operator classes. For this example an operator can only calculate two values.

//The interface for the strategies public interface ICalculateInterface { //define method int Calculate(int value1, int value2); }

Next create the operators (strategies) Minus (which subtract value 2 from value 1) and Plussus (which addition value 1 with value 2). The classes need to inherit from the interface ICalculateInterface.

//Strategy 1: Minus class Minus : ICalculateInterface { public int Calculate(int value1, int value2) { //define logic return value1 - value2; } } //Strategy 2: Plussus class Plussus : ICalculateInterface { public int Calculate(int value1, int value2) { //define logic return value1 + value2; } }

At last we need to create a Client that will execute the strategy.

//The client class CalculateClient { private ICalculateInterface calculateInterface; //Constructor: assigns strategy to interface public CalculateClient(ICalculateInterface strategy) { calculateInterface = strategy; } //Executes the strategy public int Calculate(int value1, int value2) { return calculateInterface.Calculate(value1, value2); } }

Now we have two operators (minus & plussus) and a client (CalculateClient) that can execute the operators. Let’s test the code. Create a new webapplication, console app or something else that can write output. For this example I will use a webpage.

Initialize a new CalculateClient with argument operator Minus of Plussus and Calculate two values.

protected void Page_Load(object sender, EventArgs e) { CalculateClient minusClient = new CalculateClient(new Minus()); Response.Write("<br />Minus: " + minusClient.Calculate(7, 1).ToString()); CalculateClient plusClient = new CalculateClient(new Plussus()); Response.Write("<br />Plussus: " + plusClient.Calculate(7, 1).ToString()); }

This code will give the following output.

<br />Minus: 6 <br />Plussus: 8

The great thing about this pattern is that you can easily add new opertators (strategies) to your code.

Cheers,

Pieter

very Nice Explanation

very easy to learn,

thanks

Thanks man, just what I was looking for.

It couldn’t be any clearer!

That was good. Could you please provide remaining frequently used Design patterns examples. It would be very easy for all of them to understand such simple learning. Thank you for this post.