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PHP Variable

A Variable is a small temporary memory area use to store value entered by the user, the value may be decimal number, non-decimal number, text, date, etc. In other words, variables are the "containers" for storing information.

Rules to declare a PHP variable are:
  1. A variable must starts with the '$' (dollar) sign, followed by the variable name.
  2. A variable name can contain letters, numbers, and underscores.(A-Z, a-z, 0-9, and _ )
  3. A variable name must begin with a letter or the underscore character, it cannot begin with a number.
  4. A variable name cannot contain special characters.
  5. Variable names are case-sensitive ($age and $AGE are different variables).

PHP Data Types

Data types define the type of value entered by the user. PHP has a total of 8 data-types which we use to store variable:

  1. Integer Integer contain numeric value that can be positive or negative, but without a decimal point, e.g. $var = 1234;
  2. Double Double contain numeric as well as floating-point number, e.g. $num = 2.2888855;
  3. Boolean Boolean have only two possible values either true or false. e.g. $x = true; Boolean are often used in conditional testing.
  4. NULL NULL is a special data type that only has one value:NULL. e.g. $my_var = NULL;
  5. String The string is a collection of characters, e.g. $str = "This is a string". A string can be any text inside quotes. You can use single or double quotes to represent strings.
  6. Array An array stores multiple values in one single variable. Like $colors = array("Red","Green","Blue");
  7. Object Object are instances of a class, which can package up both kinds of values and functions that are specific to the class.
  8. Resource Resource are the special variables that hold references to resources external to PHP (such as database connections).

Example 1: Some Valid Variable Declaration:

$txt = "Programming is Fun!"; //variable with string value
$a = 5; // variable with integer value
$b = 10.5; //variable with float value
$_city = "Delhi"; //variable with underscore character
$marks2 = 50; //variable name contain number

Example 2: Some In-Valid Variable Declaration:

$2marks = 50; //variable name cannot contain number.
$@city = "Delhi"; //variable name cannot contain special characters like @.
$area of circle = 50.5; //variable name cannot contain spaces.

A variable can have a short name (like a, b or any alphabet) or a more descriptive name (like name, age, areaofcircle, total_marks etc).