A function declaration part will be executed by a call to the function. Programmer has to create Function Calling part inside the respective program.
SYNTAX:
function Name ( );

The index can be assigned automatically in a collection of data set.

array(key= >value,key= >value,key= >value,etc.);
key = Specifies the key (numeric or string value = Specifies the value

1. The array() function is used to create an array.
2. In PHP,there are three types of arrays:
i). Indexed arrays - Arrays with numeric index
ii). Associative arrays - Arrays with named keys
iii). Multidimensional arrays - Arrays containing one or more arrays

It gives privilege to user to write their own specific operation inside of existing program module is called as User Defined Function.

1. Reducing duplication of code
2. Decomposing complex problems into simpler pieces
3. Improving clarity of the code
4. Reuse of code
5. Information hiding

1. PHP Parameterized functions are the functions with parameters or arguments.
2. The parameter is also called as arguments, it is like variables.
Rules:
1. The arguments are mentioned after the function name and inside of the parenthesis.
2. There is no limit for sending arguments, just separate them with a comma notation.

1. PHP has more than 700 built-in functions that perform different tasks.
2. It exists in PHP installation package.
3. It is reusable piece
4. It can either return values when called or can simply perform an operation without returning any value.

Indexed array:
An indexed array is an array that uses a numeric index to access its elements. The index is a number that starts at 0 for the first element and increases by 1 for each subsequent element.
We can create an indexed array in PHP,
(i) by enclosing a comma-separated list of values in square brackets (or)
(ii) by using the array() function.
Syntax
$array Variable=[element1, element2, element 3, ... elementN];
(or)
$arrayVariable array( element1, element2, element3.... elementN);
Examples
(a) $fruits = ['apple, "banana, 'orange'];
(b) $fruits = array('apple, "banana, 'orange');



Associative array
An associative array is a data structure that store a collection of key-value pairs. The keys are used to identify the values, and the values can be of any data type. The keys in an associative array are often called "labels" because they label or identify the corresponding values.
We can create an associative array in PHP,
(i) by enclosing a comma-separated list of key-value pairs in square brackets (or) 
(ii) by using the array() function.
Syntax

Example
$student [
"Name" => "Ram",
"Age" => 25,
"Place" => "Trichy"
];

Multidimensional Arrays:
Array containing one or more arrays is called multidimensional array. PHP accepts array with two, three four or more levels.
Example:
// A two-dimensional array
$student=array
(
array("Iniyan", 100, 96),
array("Kavin", 60, 59),
array("Nilani", 1313, 139)
);
echo ＄＄student [0][0].": Tamil Mark: ".＄student [0][1].". English mark: ".＄student [0] [2]."< br >";
echo ＄＄student [1][0].": Tamil Mark: ".＄student [1][1].". English mark: ".＄student [1] [2]."< br >";
echo ＄＄student [2}[0].": Tamil Mark:".＄student [2][1].".English mark: ".＄student [2] [2]."< br >
? >

1. User Defined Function (UDF) in PHP givesa privilege to user to write own specific operation inside of existing program module.
2. Two important steps the Programmer has to create for users define Functions are:
Function Declaration
1. User-defined Function declaration begins with the keyword "function".
2. User can write any custom logic inside the function block.
Syntax:
function functionName()
{
Custom Logic code to be executed;
}
Function Calling: 
1. A function declaration part will be executed by a call to the function.
2. Programmer has to create Function Calling part inside the respective program.
Syntax:
functionName();
Example:
function insertMsg() {
echo "Student Details Inserted Successfully!";
}
insertMsg(); // call the function
?>

Function in PHP:
A block of segment in a program that performs a specific operation such as Insert, Execute, Delete, Calculate etc.
A function is a type of sub-routine or procedure in a program.
The function can be divided into three types as follows.
(i) User defined Function
(ii) Pre-defined or System defined or Built-in Function
(iii) Parameterized Function
(i) User defined Function
PHP gives a privilege to user to write own specific operation inside of existing program module.
Two important steps the programmer has to create for users defined functions are
(a) Function Declaration
(b) Function Calling
(a) Function Declaration
A user defined function declaration begins with the keyword "Function".
User can write any custom logic inside in function block.
Syntax:
function functionName()
{
custom logic code to be executed;
}
(b) Function Calling
A function declaration part will be executed by a call to the function.
Programmer has to create function calling part inside the respective program.
Syntax:
functionName();
(ii) Pre-defined or System defined or built-in Function
Built-in functions are functions that exist in PHP installation package.
Functions can either return values when called or can simply perform an operation without returning any value.
Example:
rename_function()
This function renames original name to new name.
Parameter is also called as arguments just like variables.
Arguments are mentioned after the function name and inside the parenthesis.
There is no limit for sending arguments, just separate them with a comma notation.
Examples :
Parameterized function with one argument, two arguments respectively.
(i) function School Name ($sname)
(ii) function School Name ($sname, $strength)