Search⌘ K
AI Features
Home
Courses
Learn C#

Simple User-defined Functions

Explore how to create and invoke simple user-defined functions in C#. This lesson helps you understand function structure, naming rules, and the process of calling functions. You'll practice writing functions to make your code modular and reusable, enhancing your programming skills in C#.

We'll cover the following...

Function

We can divide a program into procedural components or modules called functions in C#. We are already familiar with the Main() function. This function can be copied and reused in a programming technique called a modular or procedural approach, also known as the divide and conquer approach. We should always try to design functions that can be reused in other programs.

Broadly, there are two types of functions, which we’ll explore in the following sections.

The structure of a function

The following slides illustrate various parts of a function definition:

A function name can only contain letters (A—Z and a—z) and the underscore symbol (_). It may also contain digits (0–9), but the function name can’t start with those. For example, Key_2 is a valid function name, but 2_key is not. Function names are case-sensitive, meaning that name, Name, and NAME are three different functions.

There are two main parts of a function definition:

  • Header: The first line ending with closing parenthesis )
  • Body: The block of statements below the function header that start with an opening brace { and end with a closing brace }

The function header contains the keywords static and void (void means that the function does not have a return value), the function name, sayHello, and the parameters in (). All statements in the function body are written as a block of code, enclosed in { and }. We cannot write the body of the function without braces.

Function call

The following program demonstrates the creation of a function and a function call.

C#
class Test
{
    static void sayHello()
    {
      System.Console.WriteLine("Hello");
    }
    static void Main()
    {
      sayHello();
    }
}

We can call a function by writing the function name, followed by () and ending with ;. In line 9, we tell the program to call the function sayHello(). This line is known as a function call or calling the function.

Example of function calls

Let’s look at the following code:

C#
class Test
{
    static void first()
    {
      System.Console.WriteLine("Now inside the function 'first'.");
    }
    static void second()
    {
      System.Console.WriteLine("Now inside the function 'second'.");
    }
    static void Main()
    {
      System.Console.WriteLine("Main program is starting here.");
      first(); //calling first function
      System.Console.WriteLine("Back in main program.");
      second(); //calling second function
      System.Console.WriteLine("Back in the main program again.");
    }
}

In the program:

  • We define two simple functions—first() and second().
  • We demonstrate the sequence of execution with the help of System.Console.WriteLine() statements.

Practice creating and calling functions

Here are a few example programs to practice creating and calling functions. By clicking the “Show Solution” button, you’ll find a program that solves the respective problem. You can copy and paste the given solution into the code widget to make sure that the output of your solution matches the given solution. There can be several ways of writing correct solutions in programming.

Function to create a multiplication table

Write a function, showTableOf4(), which displays 20 terms from the table of 4. Call your function from the Main() function to display the results.

Sample output

4 x 1 = 4
4 x 2 = 8
4 x 3 = 12
4 x 4 = 16
4 x 5 = 20
4 x 6 = 24
4 x 7 = 28
4 x 8 = 32
4 x 9 = 36
4 x 10 = 40
4 x 11 = 44
4 x 12 = 48
4 x 13 = 52
4 x 14 = 56
4 x 15 = 60
4 x 16 = 64
4 x 17 = 68
4 x 18 = 72
4 x 19 = 76
4 x 20 = 80
C#
class Test
{
    // Write your code here
    static void Main()
    {
    
    }
}