Functions In PHP

A PHP function is a piece of code that can be reused multiple times. It can take input as argument list and return value. PHP has thousands of built-in functions.
Advantages of functions :
1. Reduce code redundancy
2. Increase reuse
3. Easy to maintain.
PHP provides huge set of built-in/core functions. PHP supports anonymous functions. Arguments to functions can be passed by value or reference.

Built-In functions

PHP comes standard with many functions and constructs.
General Functions :

Function	Use	Syntax
print()	Same as echo statement	print ("This is sample output");
die()	An exit function alias. Used to terminate script and prints user message before exit	Perform_Action() or die("My Action failed");
header()	To add raw HTTP headers to send to the client browser	header("Location:http://www.letsfindcourse.com");
phpinfo()	Gives PHP interpreter settings bound to web server as a webpage. Useful in debugging/trouble shooting PHP settings	phpinfo()
exit()	Common function to terminate a script	exit(); or exit;

Variable Functions :

Function	Use	Syntax
isset()	Checks whether variable is declared and assigned a value and returns TRUE if set	echo isset($x); #FALSE
unset()	A previously set variable is unset and releases memory allocated. Returns false, if variable is not already set	$x=10; => unset($x); => echo isset($x); => #FALSE
empty()	Gives TRUE if variable is not declared or its value is FALSE or empty values	$x; => echo empty($x); => #TRUE

User Defined Functions

We can declare and call user-defined functions easily. A user-defined function declaration starts with the word function.No specific return type. Can be called by passing values or references

#Syntax
function function_name(Arguments){
              
     //   function body
       
}
#Example
function caption(){
   echo "Education and Research";
}
//invoking
caption();

Pass by value

Value of the actual argument is copied into formal parameter. Any changes to value in the function does not alter the value of actual parameter.

#Example 
function net_pay($salary, $tax){
             $taxable=$salary*$tax/100.0;
             $salary=$salary-$taxable;                
             echo "Net amount : $salary";               #Net amount : 16000
}
 $sal=20000;
 $tax_per=20;
 net_pay($sal,$tax_per);
 echo "Salary : $sal";                                        #Salary : 2000

Pass by reference

Reference of the actual parameter is passed to the function. The changes made in the function will be reflected in the value of the actual parameter

#Example 
function net_pay(&$salary, &$tax){
             $taxable=$salary*$tax/100.0;
             $salary=$salary-$taxable;
             echo "Net amount : $salary";      # Net amount : 16000
       }
$sal=20000;
$tax_per=20;
net_pay($sal,$tax_per);
echo "Salary : $sal";                  # Salary : 16000

Default argument

Default arguments are used, when user may not specify a value during invocation of the function.

#Example 
function net_pay($salary, $tax =10){
             $taxable=$salary*$tax/100.0;
             $salary=$salary-$taxable;
             echo "Net amount : $salary";
       }
//invoking the function:
$sal=20000;
$tax_per=20;
net_pay($sal,$tax_per);              # Net amount : 16000
net_pay($sal);                             # Net amount : 18000