PHP/Language Basics/Variables

A properly set-up PHP variable

 
<?php 
    $myvar = 0; 
    $yourvar = "This is my value<br />"; 
    $myvar = $yourvar; 
    $myvar = "This is now my value.<br />"; 
    echo $yourvar;
    $myvar = &$yourvar; 
    
    $myvar = "This is now my value.<br />"; 
    
    echo $yourvar;
?>

Automatic Type Conversion

 
<?
    $mystring = "12";
    $myinteger = 20;
    print $mystring + $myinteger;
?>

Calculate the variable name for simpler variables and use that name to access the value of that variable.

 
<?php
$a0 = "This";
$a1 = "is";
$a2 = "a";
$a3 = "test";
for ($i = 0; $i < 4; $i++) {
  $var = "a$i";
  echo "${$var} ";
}
?>

Numbers

 
<?
    print 6;
    print 6.3;
    print 6.30;
    print 0.4422;
    print 16.216;
    print 0;
    print -23;
    print 1298317;
    print -9912111;
    print -12.52222;
    print 0.00;
?>

Numeric Data Types

 
<?php 
$a = 5; 
$b = $a / 2; 
echo "$a / 2 = $b\n"; 

$a = 6; 
$b = $a / 2; 
echo "$a / 2 = $b\n"; 
?>

Operating on variables

 
<?php
$price = 3.95;
$tax_rate = 0.08;
$tax_amount = $price * $tax_rate;
$total_cost = $price + $tax_amount;
$username = "james";
$domain = "@example.ru";
$email_address = $username . $domain;
print "The tax is " . $tax_amount;
print "\n"; // this prints a linebreak
print "The total cost is " .$total_cost;
print "\n"; // this prints a linebreak
print $email_address;
?>

PHP 5 variable functionality.

 
<?php
  $myvar = 0;
  $yourvar = "This is my value<br />";
  $myvar = $yourvar;
  $myvar = "This is now my value.<br />";
  echo $yourvar; 
  
  $myvar = &$yourvar;
  $myvar = "This is now my value.<br />";
  echo $yourvar; 
  
  $formvar = $_POST["formvar"];
  
  if ($_SESSION["loggedin"]){
    echo "Proper login";
  } else {
    echo "You are not logged in.";
  }
?>

PHP Superglobal Arrays

 
Array         Description
 
$_COOKIE      Contains keys and values set as browser cookies
 
$_ENV         Contains keys and values set by the script"s shell context
 
$_FILES       Contains information about uploaded files
 
$_GET         Contains keys and values submitted to the script using the HTTP get method
 
$_POST        Contains keys and values submitted to the script using the HTTP post method
 
$_REQUEST     A combined array containing values from the $_GET, $_POST, and $_COOKIES superglobal arrays
 
$_SERVER      Variables made available by the server
 
$GLOBALS      Contains all global variables associated with the current script

PHP Variable Examples

 
<?php
    $myvar = "foo";             /* Assigns the string "foo" */
    $php5 = "is cool";          /* Correct Syntax */
?>

Valid and invalid variable names

 
$myvar            Correct
 
$Name             Correct
 
$_Age             Correct
 
$___AGE___        Correct
 
$9                Incorrect ; starts with a number
 
$1Name            Incorrect ; starts with a number
 
$Name1            Correct; numbers are fine at the end and after the first character
 
$_Name1           Correct
 
$Name"s           Incorrect; no symbols other than "_" are allowed

valid statements

 
<?php
   $number = "5";              # $number is a string
   $sum = 15 + $number;        # Add an integer and string to produce integer
   $sum = "twenty";            # Overwrite $sum with a string.
?>