Level: Beginners
Author: Praveen.V.Nair
Date: Friday, November 09, 2007
About the Author: https://mvp.support.microsoft.com/profile/praveen

 
Contents

• C# User defined Methods. 1
• Introduction. 2
• Datatypes. 2
• Importance Main() method. 3
• Example 1 – Main() method. 3
• Call a method from another method. 3
• Example 2 – Call a method from another method. 3
• Example 3 – Call a method from another method – object reference. 4
• Methods with return Values. 4
• Example 4 – Method with return value. 5
• Pass parameters by reference. 5
• Example 5 – Pass variable by reference. 5
• Return more than one value from a method. 6
• Example 6 – Method with multiple return values. 6
• Example 7 – Method returns class object. 7
• Method Overloading. 7
• Example 8 – Method Overloading. 8
• Infinite number of parameters. 8
• Example 9 – Pass any number of parameters to a function. 8
• At the End!. 9

Introduction

As you know a C# program is made with one or more classes. These classes contain source code to do some specific tasks. We write those code usually in small blocks called ‘methods’ or in other languages you may learn subroutines, sub programs, module or functions.

You may be already aware of built-in methods like Math.sqrt(), Math.Abs(), Console.WriteLine() etc. In this article we will discuss about user defined methods. Means, how to write a method!. Why we need to write a method?  The most common answer is – to keep a block of code which we need to use in many places of a program. We will call that block with a specific name and use it in the required places instead of writing the whole lines again and again.

In mathematics you may learned this:

y = f(x) - Here x is the input of the process and y is the output of the process and f is the function of variable x. We can simply say “y is a function of x”.

In C#, we use the same format for methods. It is:

A typical C# method example will be:

public string DisplayName(string myname)

{
      string greetings = "Good Morning " + myname;
      return (greetings + "!");
}

Examples of access modifiers are public, protected, internal, private etc.

Examples of datatypes are int, string, float, bool etc.

Access modifiers and datatypes are out of scope of this article so I stop here and continue with methods.

Datatypes

Data types used as <return datatype> as well as <datatype> of the syntax can be any C# datatype as well as user defined data types. It can be an array or object. Or even it doesn’t need to return a value.

Type: void

void is used when a method does not return a value. Note that you cannot pass a void as a parameter in a method.

Importance Main() method

Main is the mandatory method in every C# program. Whether it is a windows application or a console application, you cannot execute a program without a Main() module. We can say Main() is the starting point of a C# program.

As you know C# is a case sensitive language and note the capitalized M. I tell you this because we have lowercase main() in C/C++ languages.

There are certain rules to use Main().

·         The return types must be int or void.

·         Main() must have a static modifier

There is an optional parameter – string array which is used to get the command line parameters given. Used like this:

static void Main(string[] args)

A typical Main() method example is:

Example 1 – Main() method

// Example 1 – Main() method

// Display "Hello World"

using System;

class Program
{
    static void Main()
    {
        Console.WriteLine("Hello World");
    }
}

Call a method from another method

The next example shows how to call a method from main (or any other method)

Example 2 – Call a method from another method

// Example 2

// Call a method from another method

using System; 

class Program
{
    static void DisplayName(string myname)
    {
        Console.WriteLine("Name: " + myname);
    }
 

    static void Main()
    {
        DisplayName("Hello World");
    }
}

Here, you may noticed that I used static in the new method. That is because, you will get an error if you do not use this.

‘An object reference is required for the nonstatic field, method, or property 'Program.DisplayName(string)'

You can call only static methods from another static method. You know Main() is a static method. Otherwize you have to create an object reference to solve this. Like:

Example 3 – Call a method from another method – object reference

// Example 3

// Call a method from another method - object reference

using System; 

class Program
{
    void DisplayName(string myname)
    {
        Console.WriteLine("Name: " + myname);
    }
 

    static void Main()
    {
        Program program = new Program();
        program.DisplayName("Hello World");
    }
}

Methods with return Values

return statement is used to return a value. It is important that you must return the same datatype as you specified in the method declaration. Otherwize you will get an error like this:

Cannot implicitly convert type 'string' to 'int'

Also, it is important that you must return a value if you specified a datatype other than void in the declaration. The error you can expect is:

‘not all code paths return a value’

Here is an example of method with return value:

Example 4 – Method with return value

// Example 4

// Method with return value

using System;

class Program
{
    private static int Sum(int a, int b)
    {
        return (a + b);
    }

 
    static void Main()
    {
        Console.WriteLine("Sum = " + Sum(10, 20));
        // Console.ReadLine();

    }

}

Tip: If you test these scripts under Visual Studio, you may use Console.ReadLine() at the end of all the programs. It will let you see the output till you press enter key. Otherwize you will see a flash of command window.

Pass parameters by reference

Suppose you have a variable i and you want to increment its value by one. What you do?

i = i + 1; or i++; correct?

In the same way you can alter the value of a varilable with methods also.  You will pass the variables directly to the methods by the use of reference.  ref is the keyword. (Internally it will pass the physical address location instead and do the process in that address location instead of temperory valiables used)

Check this example:

Example 5 – Pass variable by reference

// Example 5

// Pass variable by reference

 
using System; 

class Program
{
    private static void Increment(ref int a)
    {
        a++;
    }   

    static void Main()
    {
        int xa = 10;
        Increment(ref xa);
        Console.WriteLine("xa = {0}" , xa);
    }
}

Return more than one value from a method

As you see in y = f(x), it can only return one value. In many languages this is a problem. People use many crooked ways to accomplish this. Like returning an array, using global variables, by returning class objects, using ref etc. But in C# there is an easy way to achieve this. It is called ‘out’. This way we can eliminate all the demerits of using alternate ways.

The following example shows how to use:

Example 6 – Method with multiple return values

// Example 6

// Method with multiple return values

using System; 

class Program
{
    private static void DoMath(int a, int b, out int sum, out int product, out double sqrt)
    {
        sum = a + b;
        product = a * b;
        sqrt  = Math.Sqrt(a);
    } 

    static void Main()
    {
        int sum1, product1;
        double sqrt1;

        DoMath(10,20, out sum1, out product1, out sqrt1); 

        Console.WriteLine("Sum = {0}\nProduct = {1}\nSquare = {2}" , sum1,product1,sqrt1);
    }
}

Note the usage of out. You have to use it in both declaration and calling statements.

One of the other useful features is return class objects instead of ordinary datatypes.

Example 7 – Method returns class object

// Example 7

// Method returns class object

using System; 

class Program
{
    class testclass // Inner Class
    {
        public int a;
        public int b;
    }
 

    private static testclass GetTestclassValues(int a, int b)
    {
        testclass t = new testclass();
        t.a = a;
        t.b = b;
        return t;
    }

    static void Main()
    {
        testclass test = GetTestclassValues(20, 50); 

        Console.WriteLine("testclass.a = {0}\nestclass.b = {1}" , test.a, test.b);
    }
}

Method Overloading

In Object Oriented Programming concepts, there is one concept called Polymorphism. This allows values of different datatypes to be handled using a uniform interface. Polymorphism in C# is accomplished by the term called Overloading. Practically saying – they are different methods with same method name. Such ‘a method’ is called ‘overloaded method’. When such scenario arising? A small example below:

In one of our earlier example, Sum() is a method for finding the a+b. You noticed that this takes only integer values as input and integer values as output. What happens if you try to pass a double or float value to this method? You will get two errors:

The best overloaded method match for 'Program.Sum(int, int)' has some invalid arguments

Argument '1': cannot convert from 'float' to 'int'

This can be solved by writing a new method with your parameters of desired datatypes using the same method name. Like this:

Example 8 – Method Overloading

// Example 8

// Method Overloading

using System; 

class Program
{
    private static int Sum(int a, int b)
    {
        return (a + b);
    }

    private static double Sum(double a, double b)
    {
        return (a + b);
    }

    static void Main()
    {
        Console.WriteLine("Sum = " + Sum(10.5f, 20));
    }
}

Infinite number of parameters

Think of a situation where you want to pass an unknown number of parameters. It may be 2 or 3 or any number. Here the C# solution is params.  This example will help you to reach there early.

Example 9 – Pass any number of parameters to a function

// Example 9

// Pass any number of parameters to a method

using System; 

class Program
{
    private static string ShowNames(params string[] names)
    {
        string str = string.Empty;
        for (int i = 0; i < names.Length; i++)
        {
            str += names[i] + "\n";
        }
       return str;
   }

    static void Main()
    {
        string names = ShowNames("You","Me","Them","They","We","Us");
        Console.WriteLine("Names:\n\n" + names);
    }
}

At the End!

Note that this article has not covered all the areas of topic – methods. At the time of practice one can face issues as well as inventions. Happy coding.