A function is a block of code that performs a specific task.

Suppose we need to create a program to create a circle and color it. We can create two functions to solve this problem:

• a function to draw the circle
• a function to color the circle

Dividing a complex problem into smaller chunks makes our program easy to understand and reusable.

There are two types of function:

1. Standard Library Functions: Predefined in C++
2. User-defined Function: Created by users

In this tutorial, we will focus mostly on user-defined functions.

C++ User-defined Function

C++ allows the programmer to define their own function.

A user-defined function groups code to perform a specific task and that group of code is given a name (identifier).

When the function is invoked from any part of the program, it all executes the codes defined in the body of the function.

C++ Function Declaration

The syntax to declare a function is:

returnType functionName (parameter1, parameter2,...) {
    // function body
}

Here's an example of a function declaration.

// function declaration
void greet() {
    cout << "Hello World";
}