how to create function in php

First of all, there are two types of function

• built-in Functions are shown by the language
• User-Defined Functions 

built-in Functions

• like print_r(), var_dump(), var_export()

User-Defined Functions

• which are programmed by the developer as needed

When writing your function follow these rules

1. Start with a function word 
2. Follow with function_name 
   1. can start with string or underscore 
   2. not case-sensitive
   3. can`t start with number
   4. can`t use PHP Reserved words

Syntax

function function_name(){

// any code 

}

Example 

<?php
    function say_hello(){
        echo 'hello';
    }
?>

The function is called by its name with brackets 

say_hello();

Example

<?php
    function say_hello(){
        echo 'hello';
    }
    say_hello();
?>

Output

hello