ITEC 325 - PHP (PHP Third Edition by Ullman)

Chapter 2 Lecture Notes

Based on notes by Jack Davis (jcdavis@radford.edu)

• PHP Variables
  • PHP is a dynamically typed language, so variables don't have to be declared. The type of the variable is determined by its usage in code.
  • Variable Types - boolean, integer, float, string, array, object, resource, NULL
• Variable Syntax
  • All variable names must be preceded by a dollar sign ($).
  • Following the dollar sign, the variable name must begin with either a letter (A-Z, a-z) or an underscore (_). It can't begin with a number.
  • The rest of the variable name can contain any combination of letters, underscores, and numbers.
  • May not have spaces within the name of a variable.
  • Variable names are case sensitive.
  • By convention, almost all php programmers use lower case variable names, reserving uppercase names for files, resources, and constants.
• Numbers
  • floats (actually doubles) and integers
  • valid number literals,
    12.2, 44, -1, -1.2
  • use:
    $count = 22; $ctr = 13.3; ...
• Strings
  • A string is any number of characters enclosed within a pair of either single (') or double (") quotation marks. Strings can contain any combination of letters, numbers, symbols, and spaces.
  • Double-quoted strings can also contain variables. Extrapolation (only) occurs within double quoted strings.
  • String examples:
    $str = "How are you?";
    $first_name = "John";
    $str = "How are you $first_name?";
    $date = "1/01/2010";
    $str2 = "I said, \"how are you?\"";
  • Simple example
    https://php.radford.edu/~ibarland/ITEC325/2011spring-ibarland/Lectures/php/simple.php
• Arrays
  • index array
    $arr = array("john","mary","zimbo");
    $arr[] = "betty";
  • associative array
    $crsarr = array("web"=>325, "java1"=>120);
    $crsarr["discretemath"] = 122;
• Constants
  define ("pi", 3.1415926535);
  The name of the constant is always quoted, but the value you assign to the constant is only quoted if it is a string literal. When you use a constant name in code you don't precede it with a $.
  
  <?php
  define ("PI",3.14152926535);
  echo "The constant PI holds ", PI, ";<br />"; ?>
• PHP Predefined Variables ($_SERVER array)
  https://php.radford.edu/~ibarland/ITEC325/2011spring-ibarland/Lectures/php/pre-defined-vars.php
• Booleans:
  A note on implicit boolean conversions.