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Wednesday, April 23, 2008

Variables, Type Casting and Constants in PHP

Let’s start by looking at the fundamental difference between variables in PHP and in C++:

  1. Variables in PHP need not be declared before using

  2. Variables can hold any type of values due to the fact that variable are not declared of any type, you can store any value in any variable no matter which type of value it is currently holding.

So, in the previous post (Conditional Statements if...else in PHP) when we needed a variable to hold the integer (hour of the day) we just wrote

$t=(int) date(“G”);

and suppose we now want to have a string to be stored in $t variable, we’d just have to write

$t=”PHP”;

You see, in the first statement it was an integer variable but now it’s a string. Therefore we can conclude that the type of a variable is determined by the value currently assigned to it.

PHP has the following types of data:

  • Integer
  • Float
  • String
  • Boolean
  • Array
  • Object

Since PHP takes care of data types internally so you don’t have to put much of your brain to it.

Type casting

PHP being a loosely typed language gives us a way to force different data types using type casting. Type casting, as you know is a powerful feature that C++ gives us and fortunately PHP too, and that too works in the same way.

Again form previous post’s (Conditional Statements if...else in PHP) example

$t=(int)date(“G”);

As date function returns a string, we’ve to convert it to an integer to make calculations. For this we are forcing the variable to store the returned value as an integer.

Declaring constants

Constants in PHP are declared in the following form:

define(“PI”,3.14);

It declares a constant PI with the value 3.14. the constant in UPPER CASE is just a convention (as in C++) which makes it easier to distinguish from other variables.

A few points to note

  • Variables can be of any length having letters, numbers and underscore

  • Variables and constants cannot begins with a number

  • Variables are case-sensitive. $t and $T are different.

  • Variables in PHP always start with a ‘$’ sign whereas constants DON”T.

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