PHP - Introduction to PHP Functions

Introduction to PHPIntroduction to PHP
FunctionsFunctions

To function or not to function...To function or not to function...
• Organize your code into “paragraphs” - capture a
complete thought and “name it”
• Don’t repeat yourself - make it work once and then reuse
it
• If something gets too long or complex, break up logical
chunks and put those chunks in functions
• Make a library of common stuff that you do over and
over - perhaps share this with your friends...

Built-InBuilt-In FunctionsFunctions......
• Much of the power of PHP comes from its built-in
functions
echo strrev(" .dlrow olleH");
echo str_repeat("Hip ", 2);
echo strtoupper("hooray!");
echo "n";
Hello world.
Hip Hip
HOORAY!

PHP Documentation - GooglePHP Documentation - Google

One Heck of aOne Heck of a FunctionFunction..
• PHP is a very configurable system and has lots of
capabilities that can be plugged in.
• The phpinfo() function prints out the internal configuration
capabilities of your particular PHP installation
<?php
phpinfo();
?>

Defining Your OwnDefining Your Own FunctionsFunctions
• We use the function keyword to define a function, we name the function
and take optional argument variables. The body of the function is in a
block of code { }
function greet() {
print "Hellon";
}
greet();
greet();
greet();
Hello
Hello
Hello

Choosing Function NamesChoosing Function Names
• Much like variable names - but do not start with a dollar
sign
o Start with a letter or underscore - consist of letters, numbers, and underscores ( _ )
• Avoid built in function names
• Case does not matter – but please do not take
advantage of this

ReturnReturn ValuesValues
• 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 greeting() {
return "Hello";
}
print greeting() . " Glennn";
print greeting() . " Sallyn";
Hello Glenn
Hello Sally

ArgumentsArguments
• Functions can choose to accept optional arguments. Within the
function definition the variable names are effectively "aliases" to
the values passed in when the function is called.
function howdy($lang) {
if ( $lang == 'es' ) return "Hola";
if ( $lang == 'fr' ) return "Bonjour";
return "Hello";
}
print howdy('es') . " Glennn";
print howdy('fr') . " Sallyn";
Hola Glenn
Bonjour Sally

Optional ArgumentsOptional Arguments
• Arguments can have defaults and so can be omitted
function howdy($lang='es') {
if ( $lang == 'es' ) return "Hola";
if ( $lang == 'fr' ) return "Bonjour";
return "Hello";
}
print howdy() . " Glennn";
print howdy('fr') . " Sallyn";
Hola Glenn
Bonjour Sally

Call By ValueCall By Value
• The argument variable within the function is an "alias" to the
actual variable
• But even further, the alias is to a *copy* of the actual
variable in the function call
function double($alias) {
$alias = $alias * 2;
return $alias;
}
$val = 10;
$dval = double($val);
echo "Value = $val Doubled = $dvaln";
Value = 10 Doubled = 20

Call ByCall By ReferenceReference
• Sometimes we want a function to change one of its
arguments - so we indicate that an argument is "by
reference" using ( & )
function triple(&$realthing) {
$realthing = $realthing * 3;
}
$val = 10;
triple($val);
echo "Triple = $valn";
Triple = 30

Variable ScopeVariable Scope
• In general, variable names used inside of function code, do
not mix with the variables outside of the function. They are
walled-off from the rest of the code. This is done because you
want to avoid "unexpected" side effects if two programmers
use the same variable name in different parts of the code.
• We call this "name spacing" the variables. The function
variables are in one "name space" whilst the main variables
are in another "name space"
• Like little padded cells of names - like silos to keep things
spearate

Normal Scope (isolated)Normal Scope (isolated)
function tryzap() {
$val = 100;
}
$val = 10;
tryzap();
echo "TryZap = $valn";
TryZap = 10

Global Scope (common)Global Scope (common)
function dozap() {
global $val;
$val = 100;
}
$val = 10;
dozap();
echo "DoZap = $valn";
DoZap = 100

Global Variables – UseGlobal Variables – Use
RarelyRarely
• Passing variable in as parameter
• Passing value back as return value
• Passing variable in by reference
• If you use Global Variables use really long names with
nice unique prefixes
global $LastOAuthBodyBaseString;
global $LAST_OAUTH_BODY_BASE_STRING;

Programming in MultipleProgramming in Multiple
FilesFiles

Multiple FilesMultiple 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.

IncludingIncluding files in PHPfiles in PHP
• 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");

Coping with Missing BitsCoping with Missing Bits
• Sometimes depending on the version or configuration of a
particular PHP instance, some functions may be missing.
We can check that.
if (function_exists("array_combine")){
echo "Function exists";
} else {
echo "Function does not exist";
}

SummarySummary
• Built-in functions
• Making new functions
• Arguments - pass by value and pass by reference
• Including and requiring files
• Checking to see if functions are present...

Acknowledgements / ContributionsAcknowledgements / Contributions
These slides are Copyright 2010- Charles R. Severance (www.dr-chuck.com) as
part of www.php-intro.com and made available under a Creative Commons
Attribution 4.0 License. Please maintain this last slide in all copies of the document
to comply with the attribution requirements of the license. If you make a change,
feel free to add your name and organization to the list of contributors on this page
as you republish the materials.
Initial Development: Charles Severance, University of Michigan School of
Information
Insert new Contributors and Translators here including names and dates

ThankThank You !!!You !!!
For More Information click below link:
Follow Us on:
http://
vibranttechnologies.co.in/php-classes-in-mumbai.html

PHP - Introduction to PHP Functions

Recommended

More Related Content

What's hot (20)

Viewers also liked (7)

Similar to PHP - Introduction to PHP Functions (20)

More from Vibrant Technologies & Computers (20)

Recently uploaded (20)

PHP - Introduction to PHP Functions

Editor's Notes