Function Parameters

We saw how to create a very basic function in the last lesson. We also saw that a value can be returned from a function. In this lesson, we will learn how to have a function accept parameters. Parameters can be used to change the way a function works.

Let's create a function that adds two numbers together. If we want to create a function that adds two numbers, we need to be able to pass the two numbers to the function via parameters.

function add($a, $b) {
    return $a + $b;
}

echo add(1, 2); // 3
echo add(5, 5); // 10
echo add(10, 20); // 30

In the above example, we created a function called add that takes two numbers as parameters. The function then returns the sum of the two numbers. We then call the function three times with different arguments.

Parameter vs Argument

A lot of people get confused witht the terms "parameter" and "argument".

They are often used interchangeably, but there is a difference. A parameter is a variable in the function definition. An argument is the actual value that is passed to the function.

In the example above, $a and $b are parameters. 1 and 2 are arguments. I usually say parameter even when I mean argument. So just keep that in mind.

Default Values

We can also provide default values for parameters. This means that if the argument is not passed to the function, the default value will be used instead.

function sayHello($name = 'World') {
  return "Hello $name";
}

$greeting = sayHello();
$greeting2 = sayHello('Everyone');
echo $greeting;
echo '<br>';
echo $greeting2;

In the above example, we created a function called sayHello that takes one parameter. We set the default value to World. This means that if no argument is passed to the function, the default value of World will be used.

Variable Arguments

We can also pass a variable number of arguments to a function. This is useful if we don't know how many arguments will be passed to the function. The ... is called the splat operator. If you are coming from JavaScript, it is similar to the rest operator.

function addAll(...$numbers) {
  $total = 0;
  foreach ($numbers as $number) {
    $total += $number;
  }
  return $total;
}

echo '<br>';
echo addAll(1, 2, 3, 4, 5);
echo '<br>';
echo addAll(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

In the above example, we created a function called addAll that takes a variable number of arguments. We then loop through the arguments and add them together. We then return the total.

Now that we know how to create functions, I want to add to our job listings example. We'll do that in the next lesson.