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Introduction to Variables in PHP

Computer programs usually work with some form of data. Data can be a number, a text character or a string of text characters, the digital representation of a color, or an array or matrix containing any of the above types of data.

Data is stored in memory. While a program is running, data is usually stored in RAM. When a program is not running, data is stored on a magnetic disk or on a solid state storage device. A program can also write data to a file, and extract data from a file.

Every piece of data has an address in memory. In some programming languages you might actually access data by its address in memory, but in most programming languages, a piece of data's memory address is referenced by a name that you assign to it in the program code.

The defining feature of a variable is that its value can be changed during program execution. Another form of data used by programs is constants. After you define a constant's value in program code, that value cannot be changed during program execution. I'll discus constants in a future article, in this article I'll focus on variables.

PHP supports eight types of variables

integerA number without a decimal point. Includes negative numbers
floatA number with a decimal point
stringA character or characters
booleanHas two values TRUE or FALSE
arrayHolds multiple values of the same type
objectA special data structure
resourceA special kind of data used for interacting with databases
NULLA is not initialized as far as type or value

Rules for PHP Variable Names

Variable names in PHP must follow these rules:

• Must start with a $ (dollar sign)
• Can contain letters, numbers, or underscores (_)
• The first letter after the $ cannot be a number
• Variable names are case sensitive

Variables can be Defined, Assigned, Manipulated, and Displayed

Shown below is a basic example of the use of PHP variables.

<?php

$a = 2;
$b = 3;
$c = $a + $b;
print $c;

?>

The first line of code defines a variable named $a and assigns it a value of 2. The second line defines a variable named $b and assigns it a value of 3. In the third line, the value of $a and $b are added together and the result is assigned to a variable named $c. In the last line the print method is used to display the value stored in $c.

Shown below is another example of the use of PHP variables.

<?php

$a = "Hello ";
$b = " There";
$c = $a . $b;
print $c;

?>

The first line of code defines a variable named $a and assigns it the character string "Hello". The second line defines a variable named $b and assigns it the character string " There". In the third line, the strings in $a and $b are concatenated and then assigned to a variable named $c. In the last line the print method is used to display the value stored in $c.

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