Functions in PHP
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www.hope.ac.uk Faculty of Sciences and Social Sciences
HO
PEFunctions in PHP
Stewart BlakewayFML 213blakews@hope.ac.uk0151 291 3113
www.hope.ac.uk Faculty of Sciences and Social Sciences
HO
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 ()
$today = date ("l j F" );echo $today;
• Functions that return a value do not necessarily have to be stored.
echo (date ("l j F" ));
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PEdate ()
$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));
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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\“> $txt</font><br />"); }
nSFont ("A heading",12);nSFont ("some body text");nSFont ("some more body text");
?></body></html>
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HO
PEWhat will be echoed out?
<html><head><title>Local Variables</title></head><body>
<?php
function squared($num) { $num = ($num * $num); echo ($num."<br />"); }
$num = 30;squared ($num);echo ($num."<br />");
?>
</body></html>
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HO
PEWhat will be echoed out?
<html><head><title>Local Variables</title></head><body><?php
function squared (&$num) { $num = ($num * $num); echo ($num."<br />"); }
$num = 30;squared ($num);echo ($num."<br />");
?></body></html>
www.hope.ac.uk Faculty of Sciences and Social Sciences
HO
PEWhat will be echoed out?
<html><head><title>Local Variables</title></head><body>
<?php
function squared (&$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?
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