Functions in PHP (with Examples)

What is a function

A function is a named block of code that does one job. You write it once, then call it whenever you need that job done. This keeps your program short and avoids repeating the same lines everywhere.

Define and call

Use the function keyword to define, then call it by its name with brackets.

<?php
  function sayHello() {
      echo "Hello, welcome!";
  }
  sayHello();   // calling it
?>

Defining a function does not run it — it only runs when you call it. You can call the same function as many times as you like.

Parameters and return

Parameters let you pass values in. return sends a result back.

<?php
  function add($a, $b) {
      return $a + $b;
  }
  $sum = add(5, 3);
  echo $sum;
?>

Here $a and $b are parameters; 5 and 3 are the arguments. return hands back 8, which we store in $sum.

Default parameters

Give a parameter a default value so it is optional.

<?php
  function greet($name = "Guest") {
      echo "Hi, $name";
  }
  greet("Aman");   // Hi, Aman
  echo "\n";
  greet();          // Hi, Guest
?>

When no argument is given, the default ("Guest") is used. Defaults must come after non-default parameters in the list.

Scope inside functions

Variables inside a function are local — they do not affect variables outside.

<?php
  $x = 10;
  function change() {
      $x = 99;      // a separate local $x
  }
  change();
  echo $x;          // still 10
?>

The function's $x is a different box from the outside $x. To change an outside value, return it and reassign, or pass by reference — the clean way is usually to return.

Common mistakes

• Defining but never calling. A function does nothing until you call it.
• Forgetting return. Without it the function gives back NULL, so $sum would be empty.
• Wrong argument order. Arguments fill parameters left to right — order matters.
• Expecting inside changes to affect outside variables. They are local unless returned or passed by reference.

Summary

• A function is reusable named code — define once, call many times.
• Parameters pass values in; return sends a result back.
• Default parameters make an argument optional.
• Variables inside a function are local by default.
• Functions keep code short, clear and easy to fix.

Next, use functions on text with PHP string functions, or organise data with arrays in PHP.