PHP - Data Types

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The term "data types" refers to the classification of data in distinct categories. In PHP, the following built-in data types are defined −

• integer

• double

• bool

• string

• null

• array

• object

• resource

In this chapter, let's discuss in detail about these built-in data types of PHP.

Integer

A whole number, without a decimal point (like 4195) is of int type in PHP.

• An int is a number of the set Z = {..., -2, -1, 0, 1, 2, ...}.

• An int can be represented in a decimal (base 10), hexadecimal (base 16), octal (base 8) or binary (base 2) notation.

To use octal notation, a number is preceded with "0o" or "0O". To use hexadecimal notation, precede the number with "0x". To use binary notation, precede the number with "0b". Given below are some examples −

• Decimal integer: 201, 4195, -15

• Octal integer: 0010, 0O12, -0O21

• Hexadecimal integer: 0x10, -0x100

• Binary integer: 0b10101, -0b100

double

Floating point numbers (also known as "floats", "doubles", or "real numbers") are the numbers with a fractional component. The fractional component follows after the integer component separated by the decimal symbol (.)

Standard float notation − 1.55, 21.2468, -123.0

PHP also allows the use of scientific notation to represent a floating point number with more digits after the decimal point. The symbol "E" or "e" is used to separate the integer and fractional part.

Scientific float notation − 1.2e3, 2.33e-4, 7E-10, 1.0E5 

bool

The bool type only has only two values; it can either be True or False. The bool type is used to express a truth value. Typically, the result of an operator which returns a bool value is passed on to a control structure such as "if", "while" or "do-while".

String

A string is a sequence of characters, for example, 'PHP supports string operations.'

• In PHP, a character is the same as a byte. This means that PHP only supports a 256-character set, and hence does not offer native Unicode support.

• PHP supports single quoted as well as double quoted string formation. Both the representations 'this is a simple string' as well as "this is a simple string" are valid.

• PHP also has Heredoc and Newdoc representations of string data type.

null

In PHP, null represents a special type that only has one value: NULL. Undefined and unset() variables will resolve to the value "null".

array

An array in PHP is an ordered map, a key is associated with one or more values. A PHP array is defined using the array() function, or with the use of a shorter notation where the data is pit in square brackets. These are the examples of associative arrays −

array() function

$arr = array(
   "foo" => "bar",
   "bar" => "foo",
);

Short notation

$arr = [
   "foo" => "bar",
   "bar" => "foo",
];

An array in PHP can also be defined with the "key-value pair" syntax. It is called an indexed array.

$arr = array("foo", "bar", "hello", "world");

In a multi-dimensional array, each element in the main array can also be an array. And, each element in the sub-array can be an array, and so on. Values in the multi-dimensional array are accessed using multiple index.

object

An object type is an instance of a programmer-defined class, which can package up both other kinds of values and functions that are specific to the class.

To create a new object, use the new statement to instantiate a class −

class foo {
   function bar() {
      echo "Hello World."; 
   }
}

$obj = new foo;
$obj->bar();

resource

Resources are special variables that hold references to resources external to PHP (such as a file stream or database connections).

Here is an example of file resource −

$fp = fopen("foo.txt", "w");

Data belonging to any of the above types is stored in a variable. However, since PHP is a dynamically typed language, there is no need to specify the type of a variable, as this will be determined at runtime.

Example: The gettype() Function

The gettype() function is helpful to find out the type of data stored in a variable.

<?php
   $x = 10;
   echo gettype($x) . "\n";

   $y = 10.55;
   echo gettype($y) . "\n";

   $z = [1,2,3,4,5];
   echo gettype($z) . "\n";
?>

When you run this code, it will produce the following output −

integer
double
array