How to Define a Variable in PHP | Variable in php

How to Define a Variable in PHP | Variable in php

In PHP, a variable does not need to be declared before adding a value to it. PHP automatically converts the variable to the correct data type, depending on its value.

In PHP, a variable is declared using a $ sign followed by the variable name. Here, some important points to know about variables:

As PHP is a loosely typed language, so we do not need to declare the data types of the variables. It automatically analyzes the values and makes conversions to its correct datatype.
After declaring a variable, it can be reused throughout the code.
Assignment Operator (=) is used to assign the value to a variable.

Syntax of declaring a variable in PHP is given below:

$variablename=value;

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Creating PHP Variables

In PHP, a variable starts with the $ sign, followed by the name of the variable:

Example

$txt = "Hello world!";

$x = 5;

$y = 10.5;

PHP Variable: Declaring string, integer, and float

Example to store string, integer, and float values in PHP variables.

File: variablename1.php

Example

$str="any string";

$x=500;

$y=55.6;

echo "string is: $str <br/>";

echo "integer is: $x <br/>";

echo "float is: $y <br/>";

Output:

string is: any string

integer is: 500

float is: 55.6

PHP Variable: Sum of two variables

variablename2.php

$x=5;

$y=6;

$z=$x+$y;

echo $z;

Output:

In order to use variable variables with arrays, you have to resolve an ambiguity problem. That is, if you write $$a[1] then the parser needs to know if you meant to use $a[1] as a variable, or if you wanted $$a as the variable and then the [1] index from that variable. The syntax for resolving this ambiguity is: ${$a[1]} for the first case and ${$a}[1] for the second.

Curly braces may also be used, to clearly delimit the property name. They are most useful when accessing values within a property that contains an array, when the property name is made of multiple parts, or when the property name contains characters that are not otherwise valid (e.g. from json_decode() or SimpleXML).

Example Variable property example

class foo {

var $bar = 'I am bar.';

var $arr = array('I am A.', 'I am B.', 'I am C.';

var $r = 'I am r.';

}

$foo = new foo();

$bar = 'bar';

$baz = array('foo', 'bar', 'baz', 'quux');

echo $foo->$bar . "n";

echo $foo->{$baz[1]} . "n";

$start = 'b';

$end = 'ar';

echo $foo->{$start . $end} . "n";

$arr = 'arr';

echo $foo->{$arr[1]} . "n";

Output:

I am bar.

I am r.

Rules for PHP variables:

A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
Variable names are case-sensitive ($age and $AGE are two different variables)
A variable starts with the $ sign, followed by the name of the variable
A variable name must start with a letter or the underscore character
A variable name cannot start with a number

PHP is a Loosely Typed Language

In the example above, notice that we did not have to tell PHP which data type the variable is.

PHP automatically associates a data type to the variable, depending on its value. Since the data types are not set in a strict sense, you can do things like adding a string to an integer without causing an error.

In PHP 7, type declarations were added. This gives an option to specify the data type expected when declaring a function, and by enabling the strict requirement, it will throw a “Fatal Error” on a type mismatch.

You will learn more about strict and non-strict requirements, and data type declarations in the PHP Functions chapter.

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