PHP have two types funcation available :

1 .PHP Built-in Functions

PHP has over 1000 built-in functions that can be called directly, from within a script, to perform a specific task like gettype(), print_r(), var_dump, etc.

2 .PHP User-Defined Functions

PHP user-defined function declaration starts with the function keyword :

Creating PHP Function

Its very easy to create your PHP function. Create a PHP function which will write a simple message on your browser when you will call it function. Following example creates a function called currentDate() and then calls it just after creating it.

<?php
function currentDate(){
    echo "Today Date is " . date("d-m-Y");
}
currentDate();
?>

PHP Functions with Parameters

In this function you can call function with pass arguments parameters.

<?php
    function sum($num1, $num2) {
       $sum = $num1 + $num2;
       echo "Sum of the two numbers is : $sum";
    }

    sum(10, 20);
 ?>

PHP Functions returning value

This function can return a value using the return statement with a value or object.

If sometime you want to return a value if you are using functions. This is where the return statement comes in. Let’s look at an example:

<?php
    function sum($num1, $num2) {
       $sum = $num1 + $num2;
       return $sum;
    }
    $total = sum(10, 20);

    echo "Total is : $total";
?>

Set Default Values for Function Parameters

In this function you can not pass any value at that this function set default value.

<?php
    function defaultfunction($no = 20) {
       print $no."<br />";
    }

    defaultfunction(10);
    defaultfunction();
 ?>