PHP: Hypertext Preprocessor

The Building Blocks

Special Data TypesResource - Reference to a third-party

resource (a database, for example)NULL - An uninitialized variable

Sample<?php$testing; // declare without assigningprint gettype( $testing ); // NULL?>

PHP’s Type Functions

var_dump() - tells you a variable's type and its contents

Sample<php$testing = 5; var_dump( $testing ); ?>

PHP’s Type Functionsgettype()function - to acquire the type of any

variable. If you place a variable between the parentheses of the function call, gettype() returns a string representing the relevant type (NULL, integer, string, double , boolean )

Sample<?php$testing = 5; print gettype( $testing ); // integer ?>

PHP’s Type Functionssettype()function - to change the type of a variable. To

use settype(), you must place the variable to change (and the type to change it to) between the parentheses and separate them by commas

Sample<?php$undecided = 3.14;settype( $undecided, double );print gettype( $undecided ); print " -- $undecided<br />"; // 3.14?>

Operators and ExpressionsOperators- are symbols that enable you to use one or more

values to produce a new value. A value that is operated on by an operator is referred to as an operand.4+3

 Expression- is any combination of functions, values, and

operators that resolves to a value.4+3=9$user=you;gettype( $user);

 Assignment Operator - takes the value of its right operand

and assigns it to its left operand$name = "matt";

Operators and ExpressionsArithmetic Operators - The addition operator

adds the right operand to the left operand, whereas the subtraction operator subtracts the right operand from the left. The division operator divides the left operand by the right, and the multiplication operator multiplies the left operand by the right. The modulus operator returns the remainder of the left operand divided by the right.

Example(+)Addition (-)Subtraction (/)Division (*) Multiplication (%)Modulus

Concatenation OperatorThe concatenation operator is a single period

(.). Treating both operands as strings, it appends the right operand to the left

Sample"hello"." world" is equivalent to "hello world" $centimeters = 212; print "the width is ".($centimeters/100)."

meters";

Combined Assignment Operatorconsists of a standard operator symbol

followed by an equals sign.Example$x = 4;$x = $x + 4; // $x now equals 8 can instead be written as$x = 4;$x += 4; // $x now equals 8

Comparison Operatorsperform tests on their operands. They return

the boolean value true if the test is successful and return false otherwise. This type of expression is useful in control structures, such as if and while statementsExample$x=5.1$x < 5

Logical OperatorsTo test combinations of booleans

Sampletrue || false = truetrue && false = false

Operator Precedence

When you use an operator, the PHP engine usually reads your expression from left to right.

Sample4 + 5=94 + 5 * 2 = 18 or 4 + 5 * 2 = 14 or (4 + 5) * 2 = 18

Constants Variables offer a flexible way of storing data because you can change their

values and the type of data they store at any time. If, however, you want to work with a value that you do not want to alter throughout your script's execution, you can define a constant. You must use PHP's built-in function define() to create a constant. After you have done this, the constant cannot be changed. To use the define() function, you must place the name of the constant and the value you want to give it within the call's parentheses. These values must be separated by a comma, like so:

Example

define ("CONSTANT_NAME", 42);

<?php define ("USER", "Gerald");

print "Welcome".USER;?>