PHP Unit 3 functions_in_php_2

UNIT – 3
FUNCTIONS IN PHP

Dr. P S V S Sridhar
Assistant Professor (SS)
Centre for Information Technology

| Jan 2013| © 2012 UPES

Functions
 A function is a self-contained block of statements that performs a specific
task . Functions are most useful when you need to use the same code in
more than one place. Reusing existing code reduces costs, increases
reliability, and improves consistency. Ideally, combining existing reusable
components, with a minimum of development from scratch creates a new
project. If you find that your code files are getting longer, harder to
understand, and more difficult to manage, however, it may be an
indication that you should start wrapping some of your code up into
functions.
Some of the properties of a function:
 has a unique name.
 is independent and it can perform its task without intervention from or
interfering with other parts of the program .
 can take some inputs(i.e arguments) for performing a task.
 returns a value to the calling program. This is optional and depends upon
the task your function is going to accomplish.
Jul 2012
Jan 2013 © 2012 UPES

Functions

 Functions are the heart of a well-organized script, making code easy to
read and reuse.
 The basic syntax for using (or calling) a function is:
function_name(expression_1, expression_2, ..., expression_n)
 sqrt(9); // square root function, evaluates to 3
 rand(10, 10 + 10); // random number between 10 and 20
 strlen(“This has 22 characters”); // returns the number 22
 pi(); // returns the approximate value of pi
 strrev (" .dlrow olleH"); //returns Hellow world.
 str_repeat("Hip ", 2); //returns Hip two times
 strtoupper("hooray!"); //returns in capital HOORAY
 phpinfo() function prints out the internal configuration capabilities of your particular
PHP installation

Jul 2012
Jan 2013 © 2012 UPES

Built-in Functions in PHP
 Every language has a set of built-in functions (for example, string
functions). For example: echo(“PHP”);
 print(“It is a server side programming language”);
 Some of the Array functions in PHP are:
 array() ◦ To Create an array
 sort() ◦ Sorts an array
 array_unique() ◦ Removes duplicate values from an array
 count() ◦ Counts no of elements in an array
 array_reverse() ◦ Returns an array in the reverse order

Jul 2012
Jan 2013 © 2012 UPES

Built-in Functions in PHP
 Some of the character functions in PHP are:
 ctype_upper() ◦ Checks if all of the characters in the provided string are
uppercase characters, return as 1.
 ctype_digit() ◦ Checks if all of the characters in the provided string, text,
are numerical.
 ctype_alpha() ◦ Checks if all of the characters in the provided string,
text, are alphabetic
 ctype_alnum() - Check for alphanumeric character(s)
 ctype_xdigit() - Check for character(s) representing a hexadecimal digit
 is_numeric() - Finds whether a variable is a number or a numeric string
 is_int() - Find whether the type of a variable is integer
 is_string() - Find whether the type of a variable is string

Jul 2012
Jan 2013 © 2012 UPES

User defined functions
 A function is a way of wrapping up a chunk of code and giving that chunk
a name, so that you can use that chunk later in just one line of code.
Functions are most useful when you will be using the code in more than
one place, but they can be helpful even in one-use situations, because
they can make your code much more readable.
 function function-name ($argument-1, $argument-2, ..)
{ statement-1; statement-2; ... }
 That is, function definitions have four parts:
 The special word function
 The name that you want to give your function
 The function’s parameter list — dollar-sign variables separated by
commas
 The function body — a brace-enclosed set of statements

Jul 2012
Jan 2013 © 2012 UPES

Function definition example
function better_deal ($amount_1, $price_1,$amount_2, $price_2)
{
$per_amount_1 = $price_1 / $amount_1;
$per_amount_2 = $price_2 / $amount_2;
return($per_amount_1 < $per_amount_2);
}
$liters_1 = 1.0; $price_1 = 1.59; $liters_2 = 1.5; $price_2 = 2.09;
if (better_deal($liters_1, $price_1, $liters_2, $price_2))
print(“The first deal is better! ”);
else
print(“The second deal is better! ”);

Jul 2012
Jan 2013 © 2012 UPES

Call 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";

 Output:

Value = 10 Doubled = 20
Jul 2012
Jan 2013 © 2012 UPES

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

Jul 2012
Jan 2013 © 2012 UPES

Argument number mismatches
 Too few arguments
 If you supply fewer actual parameters than formal parameters, PHP
will treat the unfilled formal parameters as if they were unbound
variables. However, under the usual settings for error reporting in
PHP6, you will also see a warning printed to the browser.
 Too many arguments
 If you hand too many arguments to a function, the excess arguments
will simply be ignored, even when error reporting is set to E_ALL.

Jul 2012
Jan 2013 © 2012 UPES

Passing Arrays to Functions
<?php
$scores = array(57,58,39,67,59);
average($scores);
function average($array)
{ $t = 0;
foreach($array as $val)
$t = $t + $val;
if(count($array > 0))
echo "The average is ", $t/count($array);
else
echo "No elements to average";
}
?>

Jul 2012
Jan 2013 © 2012 UPES

Returning Arrays
<?php
$data1 = create_array(3);
print_r($data1);
$data2 = create_array(4);
print_r($data2);
function create_array($number)
{
for($counter = 0; $counter < $number; $counter++)
{ $array[] = $counter; }
return $array;
}
?>

Jul 2012
Jan 2013 © 2012 UPES

PHP Variable Scopes
 The scope of a variable is the part of the script where the variable can
be referenced/used.
 PHP has four different variable scopes:
 local
 global
 static
 parameter

Jul 2012
Jan 2013 © 2012 UPES

Functions and variable scope
 The scope of a variable defined inside a function is local by default,
meaning that it has no connection with the meaning of any variables
outside the function.
 The syntax of this declaration is simply the word global, followed by a
comma-delimited list of the variables that should be treated that way, with
a terminating semicolon. Ex2:
<?php
 global $count1, $count2; $x=5; // global scope
Ex1: $y=10; // global scope
<?php
function myTest()
function myfunction()
{
{ global $x,$y;
$GLOBALS["n1"] = 10; $y=$x+$y;
}
}
$n1 = 20; myTest();
myfunction(); echo $y; // outputs 15
?>
echo $n1;
Jul 2012
Jan 2013 © 2012 UPES

Static variables
 The static keyword allows for an initial assignment, which has an
effect only if the function has not been called before. The first time the
variable executes initial value assigned.
 The second time the function is called, it has the value it had at the
end of the last execution.
<?php
function myTest()
{
static $x=0;
echo $x;
$x++; Output:
} 012
myTest();
myTest();
myTest();
?>
Jul 2012
Jan 2013 © 2012 UPES

Example
function SayMyABCs3 ()
{
static $count = 0; //assignment only if first time called
$limit = $count + 10;
while ($count < $limit)
{
print(chr(ord(‘A’) + $count)); // chr () converts ASCII to char ord() returns ASCII value of char
$count = $count + 1;
Output:
}
ABCDEFGHIJ
print(“ Now I know $count letters ”);
Now I know 10 letters
} Now I’ve made 1 function call(s).
$count = 0; KLMNOPQRST
SayMyABCs3(); Now I know 20 letters
$count = $count + 1; Now I’ve made 2 function call(s).
print(“Now I’ve made $count function call(s). ”);
SayMyABCs3();
$count = $count + 1;
print(“Now I’ve made $count function call(s). ”);
Jul 2012
Jan 2013 © 2012 UPES

Parameter Scope
 A parameter is a local variable whose value is passed to the function
by the calling code.
 Parameters are declared in a parameter list as part of the function
declaration:
 <?php

function myTest($x)
{
echo $x;
}

myTest(5);

?>

Jul 2012
Jan 2013 © 2012 UPES

Include and require
 It’s very common to want to use the same set of functions across a set
of web site pages, and the usual way to handle this is with either include
or require, both of which import the contents of some other file into the
file being executed. Using either one of these forms is vastly preferable
to cloning your function definitions (that is, repeating them at the
beginning of each page that uses them).
 For example, at the top of a PHP code file we might have lines like:
include “basic-functions.inc”;
include “advanced-function.inc”;
 Both include and require have the effect of splicing in the contents of
their file into the PHP code at the point that they are called. The only
difference between them is how they fail if the file cannot be found. The
include construct will cause a warning to be printed, but processing
of the script will continue; require, on the other hand, will cause a
fatal error if the file cannot be found.

Jul 2012
Jan 2013 © 2012 UPES

 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");

Jul 2012
Jan 2013 © 2012 UPES

Missing functions
 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";}

Jul 2012
Jan 2013 © 2012 UPES

Variable functions
In PHP we can assign variable value as a function name.
<?php
$function_variable = "red";
$function_variable();
$function_variable = "white";
$function_variable("In white() now");
function red()
{
echo "In red() now";
}
function white($argument)
{
echo $argument;
}
Jul 2012
Jan 2013 © 2012 UPES
?>

Nested functions
<?php or <?php
outer_function();
outer_function(); function outer_function()
{
inner_function();
echo "Outer function";
function outer_function() inner_function();
}
{ function inner_function()
{
echo "Outer function";
echo "inner function";
function inner_function() }
?>
{
echo "inner function";
}
}
?>
Jul 2012
Jan 2013 © 2012 UPES

Passing Variable Number of Arguments
 func_num_args – Returns the number of arguments passed
 func_get_arg – Returns a single argument
 func_get_args – Returns all arguments in an array
<?php
connector('How','are','things');
function connector()
{
$data = '';
$arguments = func_get_args();
for ($loop_index = 0; $loop_index <func_num_args(); $loop_index++)
$data .= $arguments[$loop_index] . ' ';
echo $data; output:
} How are things
?> Jul 2012 © 2012 UPES
Jan 2013

PHP Unit 3 functions_in_php_2

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