PHP Variables

Table of Contents

• Introduction
• Declaring PHP Variables
• Variable-naming Rules
• Integers
• Floating-point Numbers
• Booleans
• Literals vs Variables
• Variable Typing

Introduction

PHP uses variables for storing data to use in expressions and functions, and PHP supports the following standard scalar data types:

• Integers (e.g. 5 or -17).
• Floating-point numbers (e.g. 2.4 or 3.14159).
• Strings (e.g. "Hello" or 'World').
• Booleans (TRUE or FALSE).

The type of a variable is not set by the user but rather, it is decided at runtime by PHP depending on the context in which that variable is used.

In this article, we will discuss integers, floats and bools and leave strings to the next topic.

Declaring PHP Variables

PHP does not need any special keyword (such as JavaScript’s var) to declare a variable. Instead, variables in PHP are represented by a dollar sign $ followed by the name of the variable. The variable name is case-sensitive. We declare a variable by assigning the variable a value.

Example

1<?php
2    $name = "Donald Trump";
3    echo $name;
4?>

Donald Trump

In the above example, we declared the variable $name by assigning to it the string "Donald Trump".

Variable-naming Rules

When creating PHP variables, the following rules must be followed:

• variable names must begin with a dollar sign ($).
• variable names (after the dollar sign) must start with a letter or the _(underscore) character.
• variable names can contain only the characters a–z, A–Z, 0–9, and _(under score).
• variable names may not contain spaces. If a variable name must comprise more than one word, a good idea is to separate the words with the _ (underscore) character (e.g. $user_name).
• variable names are case-sensitive. The variable $High_Score is not the same as the variable $high_score.

Integers

An integer is a number of the set $\mathbb{ℤ} = \{\ldots, -2, -1, 0, 1, 2, \ldots\}.$

Example

1<?php
2    $a = 1234;
3    $b = 1_234_567; // (as of PHP 7.4.0, underscores may be used )
4    echo $a;
5    echo "<BR>";
6    echo $b;
7?>

1234
1234567

Floating-point Numbers

Floating point numbers (also known as “floats”, “doubles”, or “real numbers”) can be specified using any of the following syntaxes.

Example

1<?php
2    $a = 1.234; // decimal
3    $b = 1.2e3; // exponential notation
4    $c = 7E-10; // exponential notation
5    $d = 1_234.567; // as of PHP 7.4.0
6    echo "$a <BR> $b <BR> $c <BR> $d";
7?>

1.234
1200
7.0E-10
1234.567

ADVERTISEMENT

Booleans

A bool expresses a truth value. A basic Boolean value can be either true or false. Both are case-insensitive.

Example

1<?php
2    $foo = true; // assign the constant TRUE to $foo
3    $bar = false; // assign the constant FALSE to $bar
4    echo "$foo <BR> $bar"; // print
5?>

1

Notice that while $foo is displayed as 1, $bar does not display any value.

Example

1<?php
2    $x = true; // value = 1
3    $y = true; // value = 1
4    $z = false; // value = 0
5    echo $x + $y; // 1 + 1
6    echo "<BR>";
7    echo $x + $z; // 1 + 0
8?>

2
1

Literals vs Variables

These are the basic building blocks of PHP expressions. A literal is simply something that evaluates to itself, such as the number 68 or the string "Hello World". On the other hand, a variable evaluates to the value that has been assigned to it. The simplest PHP expression can be a single literal or variable, because both return a value.

Example

 1<?php
 2    $name = "Bruce";
 3    $age = 42;
 4    echo 73 . "<br>"; // Numeric literal
 5    echo "Hello" . "<br>"; // String literal
 6    echo true . "<br>"; // Constant literal
 7    echo false . "<br>"; // Constant literal
 8    echo $name . "<br>"; // String variable
 9    echo $age . "<br>"; // Numeric variable
10?>

73
Hello
1

Bruce
42

Note that the boolean value false returns NULL (empty). Both boolean values true and false are considered constant literals since they are predefined constants in PHP. Also, the period . is a string concatenation character.

Variable Typing

PHP is a loosely typed language. This means that variables do not have to be explicitly declared before they are used and that PHP always converts variables to the type required by their context when they are accessed.

Example

1<?php
2    $string1 = "12345";
3    $number2 = 67890;
4    echo $string1 + $number2;
5?>

80235

In this example, the string $string1 is automatically converted to a numeric variable in the third line when it is added to the number $number2.

Conversely, the same logic applies when a number is converted to a string.

Example

1<?php
2    $number = 12345;
3    echo "The value of the number is $number.";
4?>

The value of the number is 12345.