Functions in PHP

www.hope.ac.uk Faculty of Sciences and Social Sciences

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PEFunctions in PHP

Stewart BlakewayFML [email protected] 291 3113


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PESession 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


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PEWhat 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.


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PETypes 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


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PEBuilt-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?


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PEArguments!

• 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);


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PEdate ()

• 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…


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PEdate ()


• Functions that return a value do not necessarily have to be stored.

echo (date ("l j F" ));


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PEdate ()


What data type is $today ?

How could we find out?


echo (gettype($today));


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PEFunction function function

echo (gettype(date("l j F" )));

What do you think is echo’d ?


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PEDefining a function• You can define a function by using the

function statement

function function_name ($argument1, $argument2 …) {

// function code goes here}


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PEDefining a function

• What is echoed out?

<?phpfunction bigfont($txt) { echo("<h1>" . $txt . "</h1>"); }

bigfont ("Hello World!");?>


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PEtt function• Examine the following code, what

does it echo out?

function tt($num) { for ( $x=1 ; $x<13 ; $x++ ) { echo ($x . “*” . $num . “=” .

$x*$num .“<br />”); } }tt (6);


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PEMore about variables!

<html><head><title>Local Variables</title></head><body><?php$life=42;function meaningOfLife ()

{echo (“The meaning of life is”. $life);}

meaningOfLife();?></body></html>


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PEMore about variables!

<html><head><title>Global Variables</title></head><body><?php$life=42;function meaningOfLife ()

{global $life;echo (“The meaning of life is”. $life);}

meaningOfLife();?></body></html>


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PEAlternatively

<html><head><title>Local Variables</title></head><body><?php$life=42;function meaningOfLife ($arg)

{echo ("The meaning of life is". $arg);}

meaningOfLife($life);?></body></html>


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PEQuestion

• 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


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PENumbered Headings

<?php$numOfHeading=1;function numHeading ($heading)

{global $numOfHeading;echo ("<h2>" . $numOfHeading . " . " . $heading . "</h2>"

);$numOfHeading++;}

numHeading ("About Me!");echo ("<p>Stewart Blakeway<br />0151 291 3113</p>");numHeading ("Currently Teaching On");echo ("<ul> <li>Computing Concepts</li><li>Database Technology</li><li>IT Business Applications</li><li>Web Development</li><li>Network & Operating Systems</li></ul>");?>


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PEQuestion

• 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!


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PENumbered Headings Alternative

<?php

function numHeading ($heading){static $numOfHeading = 1;echo ("<h2>" . $numOfHeading . " . " . $heading . "</h2>"

);$numOfHeading++;}

numHeading ("About Me!");echo ("<p>Stewart Blakeway<br />0151 291 3113</p>");numHeading ("Currently Teaching On");echo ("<ul> <li>Computing Concepts</li><li>Database Technology</li><li>IT Business Applications</li><li>Web Development</li><li>Network & Operating Systems</li></ul>");?>


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PEMore 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


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PEReturning a result

<?phpfunction mySum($num1, $num2) { $total = $num1 + $num2; return $total; }

$myNumber = 0;$myNumber = mySum(3, 4);echo $myNumber;?>

We saw this in slides 7 and 8


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PEPassing Two Arguments

<?php

function nSFont ($txt, $size) { echo ("<font size=\"$size\" face=\"Helvetica,

Arial, Sans-Serif\“>$txt</font><br />"); }

nSFont ("A heading",12);nSFont ("some body text",3);nSFont ("some more body text",3);

?>


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PE<?php

function nSFont ($txt, $size) { echo ("<font size=\"$size\" face=\"Helvetica,

Arial, Sans-Serif\“>$txt</font><br />"); }

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 headingWarning: Missing argument 2 for nsfont() in C:\Program Files\Apache Group\Apache2\htdocs\test.php on line 6some body text

Warning: Missing argument 2 for nsfont() in C:\Program Files\Apache Group\Apache2\htdocs\test.php on line 6some more body text


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PEDefault Arguments

<html><head><title>Local Variables</title></head><body>

<?php

function nSFont ($txt, $size = 3) { echo ("<font size=\"$size\" face=\"Helvetica, Arial, Sans-

Serif\“> $txt</font><br />"); }

nSFont ("A heading",12);nSFont ("some body text");nSFont ("some more body text");

?></body></html>


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PEWhat will be echoed out?


<?php

function squared($num) { $num = ($num * $num); echo ($num."<br />"); }

$num = 30;squared ($num);echo ($num."<br />");

?>

</body></html>


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<html><head><title>Local Variables</title></head><body><?php

function squared (&$num) { $num = ($num * $num); echo ($num."<br />"); }

$num = 30;squared ($num);echo ($num."<br />");

?></body></html>


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<?php

function squared (&$joe) { $joe = ($joe * $joe); echo ($joe."<br>"); }

$num = 30;squared ($num);echo ($num."<br>");

?></body></html>


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PEChecking a function exists

<?phpfunction mySum($num1, $num2)

{ $total = $num1 + $num2; return $total;

}if (function_exists (mysum))

{$myNumber = mySum(3, 4);echo $myNumber;}

else{echo ("Function not available");}

?>


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PEWhat 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!


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PEtt function – 3 Errors

function tt($num)

for ( $x=1 ; $x<13 ; $x++ ) { echo (x . “*” . $num . “=” .

$x*$num . “<br />”); }

tt 6;


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PE3 Errors

<html><head><title>Global Variables</title></head><body><?php$life=42;function meaningOfLife () { Global $life; echo (“The meaning of life is” $life); }meaningOfLife();></body></html>


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PENumbered Headings – 3 Errors

<?php

function numHeading($heading) { fixed $numOfHeading = 1; echo ("<h2>" . $numOfHeading . " . " . $heading . "</h2>" ); $numOfHeading++; }numHeading ("About Me!");echo ("<p>Stewart Blakeway<br />0151 291 3113</p>");numheading ("Currently Teaching On");echo ("<ul><li>Computing Concepts</li><li>Database Technology</li><li>IT Business Applications</li><li>Web Development</li><li>Network & Operating Systems</li>");?>


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PEAny Questions?

Functions in PHP

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