Web Programming– UFCFB3-30-1 Lecture 19-20 Instructor : Mazhar H Malik Email : mazhar@gcet.edu.om Global College of Engineering and Technology

PHP Variables, Constants and Operators Creating PHP Pages PHP Variables, Constants and Operators

Basic PHP Variables The values stored in computer memory are called variables The values, or data, contained in variables are classified into categories known as data types The name you assign to a variable is called an identifier

PHP Variables Prefixed with a $ Assign values with = operator Example: $name = “John Doe”; No need to define type Variable names are case sensitive $name and $Name are different

PHP Variables Variables are not statically typed Integers can become floats can become strings Variable types include : Boolean Integer Float String Array Object Resource NULL

Assigned by reference, this links vars PHP Variables Assigned by value $foo = "Bob"; $bar = $foo; Assigned by reference, this links vars $bar = &$foo; Some are preassigned, server and env vars For example, there are PHP vars, eg. PHP_SELF, HTTP_GET_VARS

Displaying Variables To display a variable with the echo statement, pass the variable name to the echo statement without enclosing it in quotation marks : $VotingAge = 18; echo $VotingAge; To display both text strings and variables, send them to the echo statement as individual arguments, separated by commas : echo "<p>The legal voting age is ", $VotingAge, ".</p>";

Naming Variables The name you assign to a variable is called an identifier The following rules and conventions must be followed when naming a variable: Identifiers must begin with a dollar sign ($) Identifiers may contain uppercase and lowercase letters, numbers, or underscores (_). The first character after the dollar sign must be a letter. Identifiers cannot contain spaces Identifiers are case sensitive

Declaring and Initializing Variables Specifying and creating a variable name is called declaring the variable Assigning a first value to a variable is called initializing the variable In PHP, you must declare and initialize a variable in the same statement: $variable_name = value;

PHP Constants Constants are special variables that cannot be changed Constant names do not begin with a dollar sign ($) Use them for named items that will not change Constant names use all uppercase letters Use the define() function to create a constant define("CONSTANT_NAME", value); The value you pass to the define() function can be a text string, number, or Boolean value

Standard Arithmetic operators String concatenation with a period (.) PHP Operators Standard Arithmetic operators +, -, *, / and % (modulus) String concatenation with a period (.) $car = “SEAT” . “ Altea”; echo $car; would output “SEAT Altea” Basic Boolean comparison with “==” Using only = will overwrite a variable value Less than < and greater than > <= and >= as above but include equality

Assignment (=) and combined assignment PHP Operators Assignment (=) and combined assignment $a = 3; $a += 5; // sets $a to 8; $b = "Hello "; $b .= "There!"; // sets $b to "Hello There!"; Bitwise (&, |, ^, ~, <<, >>) $a ^ $b(Xor: Bits that are set in $a or $b but not both are set.) ~ $a (Not: Bits that are set in $a are not set, and vice versa.)

Data Types A data type is the specific category of information that a variable contains Data types that can be assigned only a single value are called primitive types

Data Types PHP is not strictly typed A data type is either text or numeric PHP decides what type a variable is PHP can use variables in an appropriate way automatically E.g. $vat_rate = 0.175; /* VAT Rate is numeric */ echo $vat_rate * 100 . “%”; //outputs “17.5%” $vat_rate is converted to a string for the purpose of the echo statement Object and Array also exist as types

Numerics Data Types PHP supports two numeric data types: An integer is a positive or negative number and 0 with no decimal places (-250, 2, 100, 10,000) A floating-point number is a number that contains decimal places or that is written in exponential notation (-6.16, 3.17, 2.7541) Exponential notation, or scientific notation, is a shortened format for writing very large numbers or numbers with many decimal places (2.0e11)

Boolean Values A Boolean value is a value of TRUE or FALSE It decides which part of a program should execute and which part should compare data In PHP programming, you can only use TRUE or FALSE Boolean values In other programming languages, you can use integers such as 1 = TRUE, 0 = FALSE

References References : Anonymous.(n.d.). Apache HTTP Server Documentation Version 2.2. Retrieved from http://httpd.apache.org/docs/2.2/. Achour, M., Betz, F. (n.d.), PHP Manual. Retrieved from http://www.php.net/download-docs.php. Anonymous. (n.d.). MySQL Reference Manual. Retrieved from http://downloads.mysql.com/docs/. Naramore, E., Gerner, J., Le Scouarnec, Y., Stolz, J., Glass, M. K. (2005). Beginning PHP5, Apache, and MySQL® Web Development. Indianapolis, IN: Wiley Publishing, Inc.