Creating and Calling Functions

A function is a named block of code that you can run whenever you want. You write it once and call it as many times as you need.

Think of a function as a recipe. You write the recipe once. Every time you want the dish, you follow the recipe instead of writing the steps again.

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<?php
function sayHello(): void
{
    echo "Hello, welcome to PHP!\n";
}

sayHello();
sayHello();

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Hello, welcome to PHP!
Hello, welcome to PHP!

The parts of a function

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function name(): returnType
{
    // the code
}

• function is the keyword that starts it.
• sayHello is the name. Follow the same rules as variable names, without the $.
• () holds the parameters (empty here).
• : void says the function returns nothing. Return types come soon.
• { ... } holds the code.

Writing the function does not run it. It runs only when you call it by name followed by brackets.

Why use functions

1. No repetition. Write the code once, use it everywhere.
2. One place to fix. If the logic changes, you change it in one spot.
3. Readable code. calculateTax() says more than ten lines of maths.
4. Easy testing. A small function is easy to check on its own.

A function can call another function

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<?php
function printLine(): void
{
    echo str_repeat("-", 20) . "\n";
}

function printHeader(): void
{
    printLine();
    echo "MY SHOP\n";
    printLine();
}

printHeader();

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--------------------
MY SHOP
--------------------

Where to define functions

In PHP you can call a function before the line where it is defined, as long as it is defined at the top level of the file (not inside an if).

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<?php
echo greet();   // works, even though greet() is defined below

function greet(): string
{
    return "Hi!";
}

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Hi!

Naming

Name functions with a verb: getUser(), calculateTotal(), isValidEmail(). Use camelCase. A good name tells you what the function does without reading it.

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<?php
function printFooter(): void
{
    echo "Copyright 2026\n";
}

printFooter();
printFooter();

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Copyright 2026
Copyright 2026