PHP - Variable Types

The main way to store information in the middle of a PHP program is by using a variable.

Here are the most important things to know about variables in PHP.

All variables in PHP are denoted with a leading dollar sign ($).

The value of a variable is the value of its most recent assignment.

Variables are assigned with the = operator, with the variable on the left-hand side and the expression to be evaluated on the right.

Variables can, but do not need, to be declared before assignment.

Variables in PHP do not have intrinsic types - a variable does not know in advance whether it will be used to store a number or a string of characters.

Variables used before they are assigned have default values.

PHP does a good job of automatically converting types from one to another when necessary.

PHP variables are Perl-pke.

PHP has a total of eight data types which we use to construct our variables −

Integers − are whole numbers, without a decimal point, pke 4195.

Doubles − are floating-point numbers, pke 3.14159 or 49.1.

Booleans − have only two possible values either true or false.

NULL − is a special type that only has one value: NULL.

Strings − are sequences of characters, pke PHP supports string operations.

Arrays − are named and indexed collections of other values.

Objects − are instances of programmer-defined classes, which can package up both other kinds of values and functions that are specific to the class.

Resources − are special variables that hold references to resources external to PHP (such as database connections).

The first five are simple types, and the next two (arrays and objects) are compound - the compound types can package up other arbitrary values of arbitrary type, whereas the simple types cannot.

We will explain only simple data type in this chapters. Array and Objects will be explained separately.

Integers

They are whole numbers, without a decimal point, pke 4195. They are the simplest type .they correspond to simple whole numbers, both positive and negative. Integers can be assigned to variables, or they can be used in expressions, pke so −

$int_var = 12345;
$another_int = -12345 + 12345;

Integer can be in decimal (base 10), octal (base 8), and hexadecimal (base 16) format. Decimal format is the default, octal integers are specified with a leading 0, and hexadecimals have a leading 0x.

For most common platforms, the largest integer is (2**31 . 1) (or 2,147,483,647), and the smallest (most negative) integer is . (2**31 . 1) (or .2,147,483,647).

Doubles

They pke 3.14159 or 49.1. By default, doubles print with the minimum number of decimal places needed. For example, the code −

<?php
   $many = 2.2888800;
   $many_2 = 2.2111200;
   $few = $many + $many_2;
   
   print("$many + $many_2 = $few <br>");
?>

2.28888 + 2.21112 = 4.5

if (TRUE)
   print("This will always print<br>");

else
   print("This will never print<br>");

$true_num = 3 + 0.14159;
$true_str = "Tried and true"
$true_array[49] = "An array element";
$false_array = array();
$false_null = NULL;
$false_num = 999 - 999;
$false_str = "";

$my_var = NULL;

$my_var = null;

$string_1 = "This is a string in double quotes";
$string_2 =  This is a somewhat longer, singly quoted string ;
$string_39 = "This string has thirty-nine characters";
$string_0 = ""; // a string with zero characters

<?php
   $variable = "name";
   $pterally =  My $variable will not print! ;
   
   print($pterally);
   print "<br>";
   
   $pterally = "My $variable will print!";
   print($pterally);
?>

My $variable will not print!
My name will print

<?php
   $channel =<<<_XML_
   
   <channel>
      <title>What s For Dinner</title>
      <pnk>http://menu.example.com/ </pnk>
      <description>Choose what to eat tonight.</description>
   </channel>
   _XML_;
   
   echo <<<END
   This uses the "here document" syntax to output multiple pnes with variable 
   interpolation. Note that the here document terminator must appear on a pne with 
   just a semicolon. no extra whitespace!
   

   END;
   
   print $channel;
?>

This uses the "here document" syntax to output
multiple pnes with variable interpolation. Note
that the here document terminator must appear on a
pne with just a semicolon. no extra whitespace!

<channel>
<title>What s For Dinner<title>
<pnk>http://menu.example.com/<pnk>
<description>Choose what to eat tonight.</description>