MSDN Documentation

Creating Your First Function

Welcome to this introductory tutorial on creating your first function. Functions are fundamental building blocks in programming, allowing you to encapsulate reusable pieces of code. This guide will walk you through the process step-by-step.

Step 1: Understand the Concept

A function is a block of organized, reusable code that is used to perform a single, related, action. Functions provide better modularity for your application and a high degree of code-reusing ability. You can define a block of code once and use it multiple times in your program.

Think of a function like a mini-program within your program. It takes some input (arguments), performs some operations, and optionally returns an output.

Step 2: Define Your Function

The syntax for defining a function can vary slightly depending on the programming language you're using. For this example, let's use a common pseudo-code or a widely understood syntax (similar to JavaScript or Python).

To define a function, you typically use a keyword (like function or def), followed by the function name, parentheses () which may contain parameters, and curly braces {} or indentation to define the function body.


function greetUser(name) {
  // This is the function body
  let message = "Hello, " + name + "!";
  return message;
}
In this example:
  • function is the keyword to define a function.
  • greetUser is the name of our function.
  • (name) indicates that this function accepts one parameter, named name.
  • The code within the curly braces {} is the function's body.
  • return message; sends the value of the message variable back to wherever the function was called.

Step 3: Call Your Function

Once a function is defined, you can execute it, or "call" it, by using its name followed by parentheses. If the function expects arguments, you provide them within the parentheses.


let userName = "Alice";
let greeting = greetUser(userName); // Calling the function
console.log(greeting); // Output: Hello, Alice!

console.log(greetUser("Bob")); // Calling directly within console.log
// Output: Hello, Bob!
When greetUser(userName) is called, the value of userName ("Alice") is passed into the function and assigned to the name parameter. The function then executes its code and returns the string "Hello, Alice!".
Pro Tip: Choose meaningful names for your functions and parameters. This makes your code easier to read and understand for yourself and others.

Step 4: Functions Without Return Values

Not all functions need to return a value. Some functions are designed to perform an action, like printing to the console or updating a UI element. In many languages, if a function doesn't explicitly have a return statement, it implicitly returns a default value (often undefined or None).


function displayMessage(message) {
  console.log("Message: " + message);
  // No explicit return statement
}

displayMessage("This is a simple message.");
// Output: Message: This is a simple message.

Next Steps