Subhasis Nayak

CMC

Php MySql part -3

Contents

Using functions

Defining functions

Arguments & parameters

Default argument values

Variable scope

Using library files

Including library files

Using functions Functions are used to do certain actions. It consists block of code.

When we call a function it runs the code and give a result,

It may takes outside values.

It may return values to outside.

When we call a function it jumps to the definition of that function

and start processing codes which are inside of the ―{}‖ and once

completes it jumps back to the next line from where it was called.

PHP contains many wide range built in functions which can be

used to do solve many tasks.

User defined function

We will put some reusable code into function and use it again

and again. Here we can change the function if we want to

change how does it work or processing the block of code.

We can maintain our code easily and quickly.

Reduce the duplication of code.

Reduce the effort and time.

Changing the function definition effect all over where it is

called.

Defining function

In php to define function we need the key word ―function‖

and then name of the function.

Here we do not need any return type. What ever we

returned by default it will get it’s data type.

But when we want to return from the function we have to

use keyword ‖return‖.

function add(int x, int y){

return (x+y);

}

An example.

Arguments & parameters When we define the function we used variables with in the

first bracket.

On that time those variables are known as parameter lists.

When we call function using variables those are calledarguments.

Well, arguments are used to pass the outside variables as localvariables of local variables of function.

If we want to use GLOBAL variable use GLOBAL keywordbefore it.

An example

Default arguments

Let’s we use 2 – parameters. If we do not pass two arguments

we will get an error.

In complex logic sometimes we do not need all the

arguments. On this case what will we do.

Thanks to PHP it provides us a feature through which we can

make our arguments default.

To write a default argument, we have to initialize the

parameters when we use them on first bracket. Let’s see.

Cont’d …..

function myFunc($a=0){

Return a;

}

echo myFunc();

As I am not passing

any argument it will

take default one.

function myFunc($a){

Return a;

}

echo myFunc();

As I am not passing

any argument it will

give an error.

Variable scope

The reason values have to be passed in to functions as

arguments has to do with variable scope—the rules that

determine what sections of script are able to access which

variables.

The basic rule is that any variables are:

Variable defined in the main body of the script cannot be used

inside a function.

any variables used inside a function cannot be seen by the main

script.

Cont’d ……

Local – variables within a function are said to be local

variables or that their scope is local to that function.

Global - Variables that are not local are called global

variables.

Local and global variables can have the same name and

contain different values.

To access global variable inside the function use keyword

‖global‖ as prefix of the variable

An example

Give output 250

Give an error

Using library files

If we want to use it again in other scripts. Rather than copy

the function definition into each script that needs to use it,

you can use a library file so that your function needs to be

stored and maintained in only one place.

A library file needs to enclose its PHP code inside <?php tags

just like a regular script; otherwise, the contents will be

displayed as HTML when they are included in a script.

To do so create a ―.php‖ file put your all functions.

Including library files

To incorporate an external library file into another script,

you use the include keyword.

The include path Setting By default, include searches only the

current directory and a few system locations for files to be

included.

If you want to include files from another location, you can

use a path to the file.

You can use the include_once keyword if you want to

make sure that a library file is loaded only once.

Cont’d …..

If a script attempts to define the same function a second

time, an error will result.

Using include_once helps to avoid this, particularly when

files are being included from other library files.let’ds do it

practically.

An example

I write a function ―add_tax‖ in ―addTax.php‖

Next write a file “useTax.php”

Use include_once/include to add like below:

include_once "addTax.php";

Then call the function “add_tax()” any where in

yourblock. I used in this way.