Functions

1. Builtin Functions

There are multitudes of functions easy to use for our application development. They can help us to process data

1. String Processing
2. Array Processing

2. User Defined Functions

Syntax

function functionName( parameter1, parameter2,...., param_n ){
    /* Any valid php code goes here */
    function_body

    return return_value;
}

Functions need not be defined before they are referenced.

Valid function

// The function can be called before the function is defined.
hello();

function hello(){

}

// 

Functions within Functions

<?php
function makeOmlet(){

    echo "Making Omlet";
    function makebreadOmlet(){
        echo "Making Breadomlet";
    }
}

// We can't call makebreadOmlet() till we make omlet
makeOmlet();

makebreadOmlet();

// Trying to call first makebreadOmlet() before calling makeOmlet() won't work.
?>

Recursive Functions

// Lets make 10 Omlets
<?php
makeOmlet( 10 );

function makeOmlet( $a ){
    if( $a > 1){
        echo " </br> Making Omlet " . $a;
        makeOmlet( $a - 1 );
    }
}
?>

Function Arguments

Information may be passed to functions via the argument list, which is a comma-delimited list of expressions. The arguments are evaluated from left to right.

### Default Arguments

// Let's make a Tea
function makeTea( $type ='lime' ){
    echo "I ll be making " . $type . " Tea in a Min.";
}

What is the output of the following code

function makeyogurt($type = "acidophilus", $flavour)
{
    return "Making a bowl of $type $flavour.\n";
}

echo makeyogurt("raspberry");

Important To Note

1. By default, function arguments are passed by value (so that if the value of the argument within the function is changed, it does not get changed outside of the function).
2. prepend an ampersand (&) to the argument name in the function definition.
3. Don't Need to prepend an ampersand (&) when you call the function.Try it! You may get error

Tips

1. PHP does not support function overloading, nor is it possible to undefine or redefine previously-declared functions.

2. Function names are case-insensitive, though it is usually good form to call functions as they appear in their declaration.

3. all array functions ($needle, $haystack). Eg. in_array($needle, $haystack)

4. all string functions ($haystack, $needle). Eg. strstr($haystack, $needle)