Faculty of Sciences and Social Sciences HOPE Functions in PHP Stewart Blakeway FML

Faculty of Sciences and Social Sciences HOPE Session Aims – How to define a function – How to call a function – Passing and Receiving Values to/from functions – Function Variables and Global Variables – Giving a function storage – Functions within Functions – Checking a function exists before calling it

Faculty of Sciences and Social Sciences HOPE What is a function? A function is a self-contained block of code that can be used time and time again. Values can be passed to functions. Functions, once finished executing can pass values back to the calling code.

Faculty of Sciences and Social Sciences HOPE Types of function There are two types of function. You have seen one type already and may or may not of known it was a function. – Built-in functions – Self defined functions

Faculty of Sciences and Social Sciences HOPE Built-in Functions echo (“Hello World!”); echo is the name of the function that you are calling. Hello World! is a string that we are passing to the function. Information that you want to pass to the function should be between the parentheses. How many built in functions are there?

Faculty of Sciences and Social Sciences HOPE Arguments! The terminology that explains the data that is to be passed to the function is called an argument. Some functions require more than one argument. my_function ($an_argument, $another_argument);

Faculty of Sciences and Social Sciences HOPE date () Date () is another example of a built in function. Lets examine how this works. $today = date ("l j F" ); echo $today; date () uses lots of symbols to represent different formats. ie: M,F,m,n,d,j,l,D,w,Y …

Faculty of Sciences and Social Sciences HOPE date () $today = date ("l j F" ); echo $today; Functions that return a value do not necessarily have to be stored. echo (date ("l j F" ));

Faculty of Sciences and Social Sciences HOPE date () $today = date ("l j F" ); echo $today; What data type is $today ? How could we find out? $today = date ("l j F" ); echo $today; echo (gettype($today));

Faculty of Sciences and Social Sciences HOPE Function function function echo (gettype(date("l j F" ))); What do you think is echo ’ d ?

Faculty of Sciences and Social Sciences HOPE Defining a function You can define a function by using the function statement function function_name ($argument1, $argument2 …) { // function code goes here }

Faculty of Sciences and Social Sciences HOPE Defining a function What is echoed out? <?php function bigfont($txt) { echo(" ". $txt. " "); } bigfont ("Hello World!"); ?>

Faculty of Sciences and Social Sciences HOPE tt function Examine the following code, what does it echo out? function tt($num) { for ( $x=1 ; $x<13 ; $x++ ) { echo ($x. “*”. $num. “=”. $x*$num.“ ”); } tt (6);

Faculty of Sciences and Social Sciences HOPE More about variables! Local Variables <?php $life=42; function meaningOfLife () { echo (“The meaning of life is”. $life); } meaningOfLife(); ?>

Faculty of Sciences and Social Sciences HOPE More about variables! Global Variables <?php $life=42; function meaningOfLife () { global $life; echo (“The meaning of life is”. $life); } meaningOfLife(); ?>

Faculty of Sciences and Social Sciences HOPE Alternatively Local Variables <?php $life=42; function meaningOfLife ($arg) { echo ("The meaning of life is". $arg); } meaningOfLife($life); ?>

Faculty of Sciences and Social Sciences HOPE Question Why not always pass variables to functions and do away with global variables? Sometimes you will want to remember a value of a variable even if a function has finished or manipulate a variable outside of a function

Faculty of Sciences and Social Sciences HOPE Numbered Headings <?php $numOfHeading=1; function numHeading ($heading) { global $numOfHeading; echo (" ". $numOfHeading. ". ". $heading. " " ); $numOfHeading++; } numHeading ("About Me!"); echo (" Stewart Blakeway "); numHeading ("Currently Teaching On"); echo (" Computing Concepts Database Technology IT Business Applications Web Development Network & Operating Systems "); ?>

Faculty of Sciences and Social Sciences HOPE Question Although the last example got the point across, Global variables should be avoided and only used as the last resort! Why do you think this is? The beauty of functions is their versatility, take the echo function as an example. This is a function of code that can be used again and again. Global variables hinder the flexibility that functions offer!

Faculty of Sciences and Social Sciences HOPE Numbered Headings Alternative <?php function numHeading ($heading) { static $numOfHeading = 1; echo (" ". $numOfHeading. ". ". $heading. " " ); $numOfHeading++; } numHeading ("About Me!"); echo (" Stewart Blakeway "); numHeading ("Currently Teaching On"); echo (" Computing Concepts Database Technology IT Business Applications Web Development Network & Operating Systems "); ?>

Faculty of Sciences and Social Sciences HOPE More than One Argument So far we have seen functions that pass one argument PHP can pass as many arguments as you define The results of an argument can be returned

Faculty of Sciences and Social Sciences HOPE Returning a result <?php function mySum($num1, $num2) { $total = $num1 + $num2; return $total; } $myNumber = 0; $myNumber = mySum(3, 4); echo $myNumber; ?> We saw this in slides 7 and 8

Faculty of Sciences and Social Sciences HOPE Passing Two Arguments <?php function nSFont ($txt, $size) { echo (" $txt "); } nSFont ("A heading",12); nSFont ("some body text",3); nSFont ("some more body text",3); ?>

Faculty of Sciences and Social Sciences HOPE <?php function nSFont ($txt, $size) { echo (" $txt "); } nSFont ("A heading“,12); nSFont ("some body text"); nSFont ("some more body text"); ?> What do you suppose would happen if the function was set to accept two arguments and only one was passed? A heading Warning: Missing argument 2 for nsfont() in C:\Program Files\Apache Group\Apache2\htdocs\test.php on line 6 some body text Warning: Missing argument 2 for nsfont() in C:\Program Files\Apache Group\Apache2\htdocs\test.php on line 6 some more body text

Faculty of Sciences and Social Sciences HOPE Default Arguments Local Variables <?php function nSFont ($txt, $size = 3) { echo (" $txt "); } nSFont ("A heading",12); nSFont ("some body text"); nSFont ("some more body text"); ?>

Faculty of Sciences and Social Sciences HOPE What will be echoed out? Local Variables <?php function squared($num) { $num = ($num * $num); echo ($num." "); } $num = 30; squared ($num); echo ($num." "); ?>

Faculty of Sciences and Social Sciences HOPE What will be echoed out? Local Variables <?php function squared (&$num) { $num = ($num * $num); echo ($num." "); } $num = 30; squared ($num); echo ($num." "); ?>

Faculty of Sciences and Social Sciences HOPE What will be echoed out? Local Variables <?php function squared (&$joe) { $joe = ($joe * $joe); echo ($joe." "); } $num = 30; squared ($num); echo ($num." "); ?>

Faculty of Sciences and Social Sciences HOPE Checking a function exists <?php function mySum($num1, $num2) { $total = $num1 + $num2; return $total; } if (function_exists (mysum)) { $myNumber = mySum(3, 4); echo $myNumber; } else { echo ("Function not available"); } ?>

Faculty of Sciences and Social Sciences HOPE What next? Seminar – More exercises, specifically defining functions and calling functions Next Lecture – This is on arrays, associate arrays, multidimensional arrays, classes, methods.. And more … don ’ t miss this as its not easy!

Faculty of Sciences and Social Sciences HOPE tt function – 3 Errors function tt($num) for ( $x=1 ; $x<13 ; $x++ ) { echo (x. “*”. $num. “=”. $x*$num. “ ”); } tt 6;

Faculty of Sciences and Social Sciences HOPE 3 Errors Global Variables <?php $life=42; function meaningOfLife () { Global $life; echo (“The meaning of life is” $life); } meaningOfLife(); >

Faculty of Sciences and Social Sciences HOPE Numbered Headings – 3 Errors <?php function numHeading($heading) { fixed $numOfHeading = 1; echo (" ". $numOfHeading. ". ". $heading. " " ); $numOfHeading++; } numHeading ("About Me!"); echo (" Stewart Blakeway "); numheading ("Currently Teaching On"); echo (" Computing Concepts Database Technology IT Business Applications Web Development Network & Operating Systems "); ?>

Faculty of Sciences and Social Sciences HOPE Any Questions?