Functions in Go

A function is a container for a few lines of code that perform a specific task.

Functions allow us to organize code by breaking it into smaller, more manageable chunks that each do one clear thing.

Here's how a function definition looks in Go:

func functionName() {
    // function body
}

There are two main components of a function:

1. The function header:

• func tells Go that we are defining a function.
• functionName is the function's name.
• Parentheses (()) appear after the name. We'll use them for parameters in later lessons.
• Curly braces ({}) contain the function body.

2. The function body:

This is the code that Go executes whenever the function is called.

Here's an example:

func sayHello() {
    fmt.Println("Hello World")
}

Calling a function

A function declaration alone does not run the code inside the function body. It only declares that the function exists.

The code inside a function runs only when the function is called.

You can call or invoke a function by typing its name followed by parentheses:

func sayHello() {
    fmt.Println("Hello World")
}

func mainFunction() {
    sayHello() // Output: Hello World
}

All of the code inside the function body is executed every time the function is called.

Capitalization = exported:

In Go, a name that starts with a Capital letter (Foo) is exported — other packages can use it. A name that starts with a lowercase letter (foo) is private to its own package. This rule applies to functions, types, and struct fields alike.

func SayHello() {} // exported (capital S) — usable from other packages
func sayHello() {} // private to this package (lowercase s)

That's why you'll see fmt.Println with a capital P in the coding tutorials: it's exported from the fmt package.

Assignment
Follow the Coding Tutorial and let's write some functions.

Hint
Look at the examples above if you get stuck.