DAY - 4
PHP - Functions
·
PHP functions are similar to other programming
languages.
·
A function is a piece of code which takes one
more input in the form of parameter and does some processing and returns a
value.
·
A function will not execute
immediately when a page loads.
·
A function will be executed by a call
to the function.
·
it has more than
1000 built-in functions like fopen() and fread() etc.
- Besides the built-in PHP functions, we can create our own functions. A user defined function declaration starts with the word "function". A function name can start with a letter or underscore (not a number). The syntax is
function functionName() {
code to be executed;
}
code to be executed;
}
PHP Functions with Parameters
·
PHP gives you option to pass your parameters
inside a function. You can pass as many as parameters your like. These
parameters work like variables inside your function.
·
Following example takes two integer parameters
and add them together and then print them.
<html>
<head>
<title>Writing PHP Function with Parameters</title>
</head>
<body>
<?php
function addFunction($num1, $num2){
$sum = $num1 + $num2;
echo "Sum of the two numbers is : $sum";
}
addFunction(10,20);
?>
</body>
</html>
·
This will display following result −
Sum of the two numbers is : 30
Passing Arguments by Reference
·
It is possible to pass arguments to functions by
reference. This means that a reference to the variable is manipulated by the
function rather than a copy of the variable's value.
·
Any changes made to an argument in these cases
will change the value of the original variable. You can pass an argument by
reference by adding an ampersand to the variable name in either the function
call or the function definition.
·
Following example depicts both the cases.
<html>
<head>
<title>Passing Argument by Reference</title>
</head>
<body>
<?php
function addFive($num){
$num +=5;
}
function addSix(&$num){
$num +=6;
}
$orignum =10;
addFive( $orignum );
echo "Original Value is $orignum<br />";
addSix( $orignum );
echo "Original Value is $orignum<br />";
?>
</body>
</html>
·
This will display following result −
Original Value is 10
Original Value is 16
PHP Functions returning value
·
A function can return a value using the return
statement in conjunction with a value or object.
·
The statement return stops the execution of the
function and sends the value back to the calling code.
·
You can return more than one value from a
function using return array(1,2,3,4).
·
Following example takes two integer parameters
and add them together and then returns their sum to the calling program. Note
that return keyword is used to return a value from a function.
<html>
<head>
<title>Writing PHP Function which returns value</title>
</head>
<body>
<?php
function addFunction($num1, $num2){
$sum = $num1 + $num2;
return $sum;
}
$return_value = addFunction(10,20);
echo "Returned value from the function : $return_value";
?>
</body>
</html>
·
This will display following result −
Returned value from the function : 30
Setting Default Values for Function Parameters
·
You can set a parameter to have a default value
if the function's caller doesn't pass it.
·
Following function prints NULL in case use does
not pass any value to this function.
<html>
<head>
<title>Writing PHP Function which returns value</title>
</head>
<body>
<?php
function printMe($param = NULL){
print $param;
}
printMe("This is test");
printMe();
?>
</body>
</html>
·
This will produce following result −
This is test
Dynamic Function Calls
·
It is possible to assign function names as
strings to variables and then treat these variables exactly as you would the
function name itself. Following example depicts this behaviour.
<html>
<head>
<title>Dynamic Function Calls</title>
</head>
<body>
<?php
function sayHello(){
echo "Hello<br />";
}
$function_holder ="sayHello";
$function_holder();
?>
</body>
</html>
·
This will display following result −
Hello
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