Functions in PHP

What is a Function?
      Function is a independent set of code statements, written to perform some tasks.


Function may or may not accept / return a value.


Function names are case-insensitive in PHP.


In PHP there are mainly 2 types of Function.


1) built-in (ready to use)
2) user-defined (created by user)


Why to use a Function?


Functions are written mainly because of reusability.(Write once and use forever)


Functions are easy to manage, simple to read.


How to use a Function?


Syntax:
function uniquename (arguments)
{
//some code
return value/variable; // optional return statement
}


The uniquename can be any string that starts with a letter or underscore.



Function Arguments / Parameters:


Depending on type, Parameters to a function can be passed in 2 ways.


Call by Value:


copy of variables are passed as parameters. hence original value is not changed.


<?php
function addthem( $n1, $n2)
 {
   $sum = $n1 + $n2;
  return $sum;
 }


 echo " Addition = " .addthem(123,321);
?>
Call by Reference:


Address of variables are passed as parameters, hence original value may be changed.


<?php
function swapthem(&$n1,&$n2) 
{
$temp=$n1;
$n1=$n2;
$n2=$temp;
}
$a=11;
$b=33;
echo "Before swap : a=".$a ." and  b = $b<br/>";
swapthem($a,$b);
echo "After swap : a=".$a ."  and  b = $b<br/>";
 ?>