functions in php

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Function In Php

By: Muhammad Baqar Qazi.


BREAKING YOUR CODE APART


calculateArea

createMessage

animateImage

get window heightget window widthcalculate areastore areaDo calculationCheck valueOutput messageGet image positionCalculate new valueSet image positionChange text colorIf position correct output message


• Often scripts need to perform the same actions in several different locations in the script.

• It may even be the case that you use the same code in different scripts.

• If you find yourself typing the same ten lines of code over and over (or cutting and pasting it repeatedly).

• you can move that code into a separate file and get it from that file whenever you need it.

• You can reuse code in two ways: by inserting a file containing code into a script or by writing and calling a function.

REUSING PHP CODE


echo “This code is inside the function”;// loops, if statements, anything!// …

{

}

function name

createMessagehideMenuanimateImagecalcuateScoremyFunction ()

//sometime lattermyFunction();myFunction();myFunction();

If it’s in function, it won’t run unless you call it

FUNCTION IN PHP


FUNCTION NAMES

• Much like variable names, but do not start with a dollar sign.

• Start with a letter or underscore - consist of letters, numbers, and underscores( _ ).

• Avoid built in function names


myFunction();

function myFunction(){//lots of codemyOtherFunction();

}

function myOtherFunction(){//lots of code

}

WHERE TO DECLARE FUNCTIONS


• You pass values to a function by putting the values between the parentheses when you call the function

functionname(value1,value2,...);

• The function statement includes variable names for the values it’s expecting,

• as follows:function functionName($varname1,$varname2,...){

statements

}

PASSING VALUES TO A FUNCTION


• The function receives the values in the order they are passed.function functionx($x,$y,$z){

//do stuff

}• You call the function as follows:

functionx($var1,$var2,$var3);

• The function sets • $x=$var1, $y=$var2, and $z=$var3.

PASSING VALUES IN THE CORRECT ORDER


• A function is designed to expect a certain number of values to be passed to it.

• If you don’t send enough values, the function sets the missing one(s) to NULL.

• If you send too many values, the function ignores the extra values.

PASSING THE RIGHT NUMBER OF VALUES


• You can set default values to be used when a value isn’t passed.

• The defaults are set when you write the function.

function add_2_numbers($num1=1,$num2=1){

echo $total = $num1 + $num2;

}

DEFAULT VALUE OF PARAMETER


• Often a function will take its arguments, do some computation and return a value to be used as the value of the function call in the calling expression. The return keyword is used for this.

function sum ($value1, $value2) {

$result = $value1+ $value2;return $result;

}echo sum();

RETURN VALUE


• You pass the copy of values to the function• The variable outside the function remains unaffected• function increment_value($y)

{ $y++; echo $y;

} $x = 1;increment_value($x); // prints ‘2’

echo $x; // prints ‘1’

PASSING ARGUMENTS BY VALUE


• You can pass a variable by reference to a function so the function can modify the variable.

• Sometimes we want a function to change one of its arguments - so we indicate that an argument is "by reference" using ( & )

• function increment_value($y) {

$y++; echo $y;

} $x = 1;increment_ reference($x); // prints ‘2’echo $x; // prints ‘2’

PASSING ARGUMENTS BY REFERENCE


• You can create and use a variable inside your function.

• Such a variable is called local to the function A local variable is not available outside of the function.

• If you want to use the variable outside the function, you have to make the variable global, rather than local, by using a global statement.

USING VARIABLES IN FUNCTIONS


• Similarly, if a variable is created outside the function, you can’t use it inside the function unless it is global.

$first_name = “Jess”;$last_name = “Jones”;function format_name(){

global $first_name, $last_name;$name = $last_name.”, “.$first_name;echo “$name”;

}format_name();

USING VARIABLES IN FUNCTIONS


Programming in Multiple Files


• When your programs get large enough, you may want to break them into multiple files to allow some common bits to be reused in many different files.

MULTIPLE FILES


• include "header.php"; - Pull the file in here• include_once "header.php"; - Pull the file in here

unless it has already been pulled in before• require "header.php"; - Pull in the file here and die

if it is missing• require_once "header.php"; - You can guess what

this means...• These can look like functions -

require_once("header.php");

INCLUDING FILES IN PHP

functions in php

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