Functions in php

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Function In Php
By: Muhammad Baqar Qazi.

BREAKING YOUR CODE APART

calculateArea
createMessage
animateImage
get window height
get window width
calculate area
store area
Do calculation
Check value
Output message
Get image position
Calculate new value
Set image position
Change text color
If 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 latter
myFunction();
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 code
myOtherFunction();
}
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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