DataType2

Integers: 
They are whole numbers, without a decimal point, like 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, like so:
<?php
$int_var = 12345;
echo $int_var; // output 12345
?>
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 like 3.14159 or 49.1. By default, doubles print with the minimum number of decimal
places needed. For example, the code:

<?php
$d1 = 2.2888800;
$d2 = 2.2111200;
$sum = $d1 + $d22;
print(.$d1 + $d2 = $sum<br>.);
?>

output:
2.28888 + 2.21112 = 4.5

Boolean:
They have only two possible values either true or false. PHP provides a couple of constants
especially for use as Booleans: TRUE and FALSE, which can be used like so:

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

Interpreting other types as Booleans: 

•   If the value is a number, it is false if exactly equal to zero and true otherwise. 
•  If the value is a string, it is false if the string is empty (has zero characters) or is the string "0", and is true otherwise. 
•   Values of type NULL are always false. 
•   If the value is an array, it is false if it contains no other values, and it is true otherwise. 
• For an object, containing a value means having a member variable that has been assigned a value. 
•   Valid resources are true (although some functions that return resources when they are successful will return FALSE when unsuccessful). 
•   Don't use double as Booleans. 

NULL
NULL is a special type that only has one value: NULL. To give a variable the NULL value, sim assign it like this:
$my_var = NULL;
The special constant NULL is capitalized by convention, but actually it is case insensitive; you
could just as well have typed:
$my_var = null;

A variable that has been assigned NULL has the following properties:

•   It evaluates to FALSE in a Boolean context. 
•   It returns FALSE when tested with IsSet() function. 

Strings:
They are sequences of characters, like "PHP supports string operations". Following are valid examples of string

$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