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Classes:

Methods (functions)

While properties and fields can be considered passive parts of a class, methods are active. They will perform one or several actions and optionally return a result. In other programming languages they are sometimes referred to as functions or even "funcs", but in C#, where they belong to a class, they are called methods. Methods are very useful because they allow you to encapsulate a piece of functionality in a method which you can then call again from several places.

A method is defined like this:

<visibility> <return type> <name>(<parameters>)
{
    <method code>
}

Here's a very basic example:

public int AddNumbers(int number1, int number2)
{
	return number1 + number2;
}

This very basic method will add two numbers and return the result. Let's step through the various parts of it:

  • public is the visibility (more on that later in this tutorial)
  • int is the return type. If you don't want your method to return anything, use the void keyword instead
  • AddNumbers is the name of the method
  • (int number1, int number2) - these are the parameters (more on those later). Parameters are optional, so you are free to leave the space between the parentheses empty. The parentheses are not optional though.
  • Inside the method (between the curly braces), you will find the actual code of the method. It can be one or many lines of code.

To call a method, simply write it's name followed by a set of parentheses. Inside the parentheses, you should write the parameters (if the method accepts any), like this:

AddNumbers(3, 39);

Since methods are defined on classes, you may want to call a method on another class than the one you are currently in. If so, you should prefix the method call with the name of the object, or in case of a static method (more on those later), the name of the class. Here's an example where we call the AddNumbers() method, which has been placed in another class called MathHelper:

public void DoMath()
{
	MathHelper mathHelper = new MathHelper();
	int result = mathHelper.AddNumbers(4, 38);
	Console.WriteLine(result);
}	

Method return types

Let's talk more about return types. In the examples above, we defined a method with an integer as the return type, but you are free to return any other kind of C# data type. In fact, you can even declare a method which doesn't return anything, as we saw with our DoMath() method above. Notice that I have substituted int with the void keyword, which means that this method is not supposed to return anything. In some programming languages, functions without a return type are referred to as procedures, but in C#, they are always called methods.

You should be aware that when you declare a return type for a method, you HAVE to return something - otherwise, the compiler will immediately complain:

public int AddNumbers(int number1, int number2)
{
	Console.WriteLine(number1 + number2);
}
Compiler error: AddNumbers(int, int)': not all code paths return a value

This means that you need one (or several) return keywords inside your method if it has a declared return type. You may need more than one for situations where you have multiple possible code paths, like this:

public int AddLargeNumbers(int number1, int number2)
{			
	if((number1 > 1000) && (number2 > 1000))
	{
		return number1 + number2;
	}
	return 0;
}

In this case, we need the second return statement as well - if it's omitted, the compiler will complain, because our conditional statement could prevent the first return statement from being hit.

Summary

Methods allow you to encapsulate and reuse functionality from several places. By supplying different parameters to a method, you can get different results. We have used some parameters in the examples above, but in the next article, we'll dig much deeper into the subject of method parameters.

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