More Arrays, Strings, and Session Variables

Associative Arrays

PHP allows you to create other kinds of arrays in addition to the ones that you have already seen. One other kind of array in PHP is the associative array.

The indices in an associative array are strings.

Consider an array that stores the names of capital cities for some states. You could, of course, use a normal array to store the city names. But it would be difficult to keep track of the relationship between the state (name) and the city name in a normal array. What if you could use the state name as the index of the array? Well, you can do this with an associative array!

This Capital Cities page demonstrates the basics of using an associative array. Actually, the page has two associative arrays, and shows you two different ways to create an associative array. The first array is for states, and the second array is for countries of the world.

The code for the Capital Cities page is shown below. This is file assoc.php:

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <link type="text/css" rel="stylesheet" href="PHPstyles.css">
  <title>Associative array demo</title>
</head>

<body>
  <div id="mainDiv">
    <h1>Associative Array Demo</h1>

    <?php
    $stateCap["Alaska"] = "Juneau";
    $stateCap["Indiana"] = "Indianapolis";
    $stateCap["Michigan"] = "Lansing";

    if (array_key_exists("Alaska", $stateCap))
    {
      print "Alaska: ";
      print $stateCap["Alaska"];
      print "<br /><br />";
    }

    $worldCap = array(
      "Albania"=>"Tirana",
      "Japan"=>"Tokyo",
      "United States"=>"Washington DC"
      );

    if (array_key_exists("Japan", $worldCap))
    {
      print "Japan: ";
      print $worldCap["Japan"];
      print "<br /><br />";
    }

    foreach ($worldCap as $country => $capital){
      print "$country: $capital<br />\n";
    } // end foreach

    ?>
  </div>
</body>
</html>

Please note these points about the above code:

The $stateCap array is built by simply creating each element in turn. The index for each element is a state name, as a string.
The $worldCap array is built by using the array( ) built-in function. But the syntax is different from the syntax that you saw last week, when we used array( ) to create a normal array (with numeric indices).
The => operator is a special assignment operator which creates a "holds" relationship, as in "Japan" holds "Tokyo". In the context of the array( ) function, it tells PHP to generate an element with, for instance, the index "Japan" which stores the value "Tokyo".
The array_key_exists( ) function calls in this code are a bit of overkill, but in the real world you can use this function to make sure that a particular key value is even in an associative array before you use that key value. The arguments to array_key_exists( ) are:
- Key (index) to look for
- Array to look in to see if the key exists
The function array_key_exists( ) returns TRUE if the key exists in the array, and FALSE if the key does not exist in the array.
When you use a foreach statement with an associative array, the syntax is a bit different from what we saw earlier in this handout, also. The first variable after the as keyword contains the index, and the second variable (which follows the => operator, of course) contains the value for each element for each iteration through the loop.
PHP does not guarantee that the elements in an associative array will be returned in any particular order when you use the foreach statement.

By the way, an associative array is used automatically by PHP to store the information that comes into a PHP page from an HTML form. The name of each of the form's elements is the index, and the value in each element is, of course, the value of the array element. If the form's method attribute is "post", the associative array in the form's action page is the familiar variable $_POST, which you have seen before. See the next section for more information.

foreach Loops

We saw for loops in the previous handout. The present handout will start off by explaining an even handier kind of loop for handling arrays: The foreach loop.

This Array Key page shows a regular for loop for review, and then demonstrates the basics of using a foreach loop.

The code for the Array Key page is shown below. This is file ArrayKey.php:

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <link type="text/css" rel="stylesheet" href="PHPstyles.css">
  <title>Some Loops</title>
</head>

<body>
  <div id="mainDiv">
    <h1>Some Loops</h1>

    <?php

    $numbers = array(125, 256, 1047, -354, 2, 0, 10000);
    $greekLetters = array("letterOne" => "alpha", "letterTwo" => "beta", "letterThree" => "gamma", "letterFour" => "delta", 
	    "letterFive" => "epsilon");
    print "<h3>A Regular for loop:</h3>\n";
    print "<ul>\n";
	for ($i = 0; $i < count($numbers); $i++)
	{
	  print "  <li>The index is " . $i . " and the value is " . $numbers[$i] . "</li>\n";
	}
    print "</ul>\n";
	
    print "<h3>A foreach loop:</h3>\n";
    print "<ul>\n";
    foreach ($greekLetters as $letterOrder => $letterValue){
	  print "  <li>The key is " . $letterOrder . " and the value is " . $letterValue . "</li>\n";
    } // end foreach loop
    print "</ul>\n";

    ?>
  </div>
</body>
</html>

Please note these points about the above code:

We use the array( ) built-in function to create some arrays.
- The array $numbers is a standard numeric-indexed array.
- The array $greekLetters is an associative array of the first five Greek letters.
The first parameter in the foreach statement is an array. In this code, the array is our $greekLetters variable.
The keyword as is followed by the name of a variable that will contain each array element's key, one at a time; followed by the "=>" operator; followed by a variable which will contain each element's value, one at a time; during each of the loop's iterations. The variables in this code are $letterOrder and $letterValue.

Built-in Associative Arrays

PHP automatically creates some associative arrays when your page loads into the PHP server (and is eventually sent as an HTML page to your browser). Some of these associative arrays are:

$_REQUEST -- HTTP Request variables. This array includes, by default, the contents of the $_POST, $_GET, and $_COOKIE arrays (see below).
$_POST if the method attribute in an HTML <form> tag is "post", and the form has been submitted.
$_GET if the method attribute in an HTML <form> tag is "get", and the form has been submitted.
$_FILES if you upload any files to the PHP server.
$_COOKIE if you are using any cookies.
$_SESSION if you are using any SESSION variables. See the last section in this handout for some information about SESSION variables.
$_SERVER is a collection of Server and execution environment information.

This Form Reader page demonstrates one very handy way to read the information that comes into your PHP page from an HTML form.

The code for the HTML form page is shown below. This is file sampleForm.html:

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <link type="text/css" rel="stylesheet" href="PHPstyles.css">
  <title>Sample Form</title>
</head>
<body>
  <div id="mainDiv">
    <h1>Sample form</h1>
    <form action="formReader.php" method="post">
    <table>
    <tr>
      <td>Name</td>
      <td>
        <input type = "text"
               name = "name" />
      </td>
    </tr>

    <tr>
      <td>Email</td>
      <td>
        <input type = "text"
               name = "email" />
      </td>
    </tr>

    <tr>
      <td>Phone</td>
      <td>
        <input type = "text"
               name = "phone" />
      </td>
    </tr>

    <tr>
      <td colspan="2">
        <input type = "submit"
               value = "Send the Form Data" />
      </td>
    </tr>
    </table>
    </form>
  </div>
</body>
</html>

The code for the Form Reader page is shown below. This is file formReader.php:

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <link type="text/css" rel="stylesheet" href="PHPstyles.css">
  <title>Form Reader</title>
</head>
<body>
  <div id="mainDiv">
    <h1>Form Reader</h1>
    <h3>Here are the fields I found in the $_REQUEST array:</h3>
    <?php
    print <<<HERE
    <table>
    <tr>
      <th>Field</th>
      <th>Value</th>
    </tr>
HERE;

    foreach ($_REQUEST as $field => $value){
      print <<<HERE
      <tr>
        <td>$field</td>
        <td>$value</td>
      </tr>
HERE;
    } // end foreach
    print "</table>\n";

    ?>
  </div>
</body>
</html>

Please note these points about the above code:

The $_REQUEST associative array may contain other elements in addition to those that belong to your form.
You can use the $_POST associative array if you want to make sure you get only the form's elements. Just make sure that you put the attribute
```
method="post"
```
into the <form> tag on the form page.

String Functions

PHP has a large number of string manipulation functions built in.

This Pig Latin page demonstrates how to use some of these built-in string functions.

The code for the Pig Latin page is shown below. This is file pigify.php:

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <link type="text/css" rel="stylesheet" href="PHPstyles.css">
  <title>Pig Latin Generator</title>
</head>
<body>
  <div id="mainDiv">
    <h1>Pig Latin Generator</h1>
    <?php
    if (!isset($_POST["inputString"]) || $_POST["inputString"] == ""){
      print <<<HERE
      <form action="pigify.php" method="post">
      <textarea name = "inputString"
                rows = "20"
                cols = "40"></textarea>
       <input type = "submit"
              value = "pigify" />
       </form>
       
HERE;
    } else {
      //there is a value, so we'll deal with it
      $inputString = $_POST["inputString"];
      //break phrase into array
      $words = explode(" ", $inputString);
      $newPhrase = "";
      foreach ($words as $theWord)
      {
        $theWord = rtrim($theWord);
        if ($theWord != "")
        {
          $firstLetter = substr($theWord, 0, 1);
          $restOfWord = substr($theWord, 1, strlen($theWord)-1);
          //print "$firstLetter) $restOfWord  \n";
          if (strstr("AEIOU", strtoupper($firstLetter)))
          {
            //it's a vowel
            $newWord = $theWord . "way";
          }
          else
          {
            //it's a consonant
            $newWord = $restOfWord . $firstLetter . "ay";
          } // end if
          $newPhrase = $newPhrase . $newWord . " ";
        }
      } // end foreach
      print $newPhrase;

    } // end if
      
    ?>
  </div>
</body>
</html>

Please note these points about the above code:

The order in which you place the two expressions in an if statement which uses the "OR" logical operator ( || ) to join the two expressions, is important. You should test for the existence of the variable with the isset() built-in function first, then after the || operator test the value in that variable. This is the order of the expressions in this line of code above:
```
if (!isset($_POST["inputString"]) || $_POST["inputString"] == ""){
```
The explode( ) built-in function breaks the string that was received from the form, into an array. It breaks the string at a "delimiter", or separator character. In this page, the delimiter is a space. So the first argument to explode( ) is a delimiter, and the second argument is the string to break up.
The code uses foreach to loop through the $words array and to process each word, one word at a time.
The rtrim( ) built-in function removes the space character from the end of the word that is being worked on. Actually, rtrim( ) also removes any tabs, newlines, and other white-space characters from the right side of the string (word).
PHP also has ltrim( ) and trim( ) built-in functions. The ltrim( ) function removes whitespace from the left side of a string. The trim( ) function removes whitespace from both ends of a string.
The substr( ) built-in function is used to get a portion of a string from a string. The substr( ) function requires three parameters:
1. The string that you want to get the portion from;
2. The character (index) that you want to start with; and
3. How many characters you want to extract from the string.
In this code, substr( ) is first used to get the first letter from the beginning of the word.
Then substr( ) is used to get the rest of the word after the first character.
The strlen( ) built-in function returns the number of characters in a string, as a number.
The strstr( ) built-in function searches for the occurrence of one string in another string. It takes two parameters:
1. The string you are searching in (sometimes called the haystack); and
2. The string you are seaching for (sometimes called the needle).
strstr( ) returns FALSE if the string you are searching for is not found in the string you are searching in.
It returns the found string, if the string you are searching for is found in the string you are searching in. This return string is interpreted by PHP as a TRUE return. See the next item for a more detailed explanation of this TRUE interpretation.
When PHP is deciding if a logical expression is TRUE or FALSE, the following values are considered to be FALSE:
- the boolean FALSE itself;
- the integer 0 (zero);
- the float 0.0 (zero);
- an empty string, and the string "0";
- an array with zero elements;
- a few other special values that are listed in the language reference manual in the section "Converting to boolean".
Every other value is considered TRUE. This is a very important fact, and this fact is why the expression
```
if (strstr("AEIOU", strtoupper($firstLetter)))
```
in the above code returns TRUE if one of the letters (vowels) is found in the haystack, because a character (a string with a single character in it) is not "0" or an empty string.
The strtoupper( ) function converts the characters in the argument's string to upper case characters.
The string concatenation (addition) operator in PHP is the period (.). String concatenation is much faster than string interpolation, by the way.

Session Variables

Session variables can be used to store information between page loads during the current user session (while their browser is still open).

Session variables are stored in the $_SESSION associative array. This array is stored in the PHP server's memory, so it retains its values even after a PHP page has been loaded and/or closed.

In the following sample code, we will use a session variable to keep unwanted visitors out of our site's main index page.

You can see what happens if you go to the index page without logging in, here. Briefly, what happens is that you are redirected to a "login" form page. (When you are ready to try logging in, the username is nosmo and the password is king)

First, here is the page which we are protecting from unwanted access. It is index.php:

<?php
  session_start();
  if (!isset($_SESSION["fakeLogin"]) || $_SESSION["fakeLogin"] != "success")
  {
    $filename = "PHPStuff/Sessions/fakeLogin.php";
    header("Location: http://" .$_SERVER['HTTP_HOST']. "/" . $filename);
  }
?>
<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <title>Main Index Page</title>
  <link rel="stylesheet" type="text/css" href="../PHPstyles.css" />
</head>

<body>
  <div id="mainDiv">
    <h3>
      This is the Fake Web Site's index page.
    </h3>
    <p>
      Lorem ipsum dolor sit amet, consectetur adipiscing elit. Curabitur accumsan 
      lacus vitae mi consequat, quis auctor lacus maximus. Nulla dolor magna, 
      elementum ut interdum eget, venenatis a quam. Proin vel purus gravida, 
      consequat quam eu, interdum risus. Ut bibendum sagittis suscipit. Sed 
      eleifend ullamcorper diam vel varius. Etiam luctus, erat.
    </p>
    <a href="fakeUnset.php">Log Out</a>
  </div>
</body>
</html>

Now, here is the HTML form page that you are redirected to: This is page fakeLogin.php:

<?php
  session_start();
?>
<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <link rel="stylesheet" type="text/css" href="../PHPstyles.css" />
  <title>Fake Login Page</title>
  <script type="text/javascript">
  	function positionCursor()
  	{
  		document.getElementById("username").focus();
  	}
  </script>
</head>

<body onload="positionCursor();">
  <div id="mainDiv">
    <?php
      if (isset($_SESSION["fakeLogin"]) && $_SESSION["fakeLogin"] == "error")
      {
        echo '<h3>You entered invalid login credentials.  Please try again.</h3>';
      }
    ?>
    <form name="theForm" action="fakeLoginAction.php"
          method="post">
      Please enter your login/user name:
      <input type="text" name="username" id="username" />
      <br />
      <br />
      Please enter your password:
      <input type="password" name="thepwd" id="thepwd" />
      <br />
      <br />
      <input type="submit" value="Log In" />
    </form>
  </div>
</body>
</html>

The login action page is fakeLoginAction.php:

<?php
session_start();
// In the real world, the password would be looked up in a database.
// If the password is correct, the session variable would be set.
// If the password is incorrect, the user would be redirected back
//   to the login form page.
// For this fake login demo, the username is "nosmo" and the password is "king".

$username = $_POST["username"];
$password = $_POST["thepwd"];

if ($username == "nosmo" && strcmp($password,"king") == 0)
{
  $_SESSION["fakeLogin"] = "success";
  $filename = "PHPStuff/Sessions/index.php";
  header("Location: http://" .$_SERVER['HTTP_HOST']. "/" . $filename);
}
else
{
	$_SESSION["fakeLogin"] = "error";
  $filename = "PHPStuff/Sessions/fakeLogin.php";
  header("Location: http://" .$_SERVER['HTTP_HOST']. "/" . $filename);
}
?>

If you look back at the code for the index page, you will see that there is a "Log Out" link on it. If you click that link, the page which unsets (resets) the session variable is fakeUnset.php. Here is that page:

<?php
session_start();
// Use this page to unset the fake session variable which is used for fakeLogin.php
error_reporting(-1);
unset($_SESSION["fakeLogin"]);

?>

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <link rel="stylesheet" type="text/css" href="../PHPstyles.css" />
  <title>Fake Login Reset/Unset</title>
</head>

<body>
  <div id="mainDiv">
	  <h3>The fake session variable has been reset/unset</h3>
	  <a href="index.php">Display the index page again</a>
	</div>
</body>
</html>

Please note these points about the above code:

This login code is a total fake. In the real world, you would compare the user's username and password with some database fields, probably, to decide if the user has given the proper information. In this fake code, we are logging in the user with fake username and password info.
The PHP function session_start() must be called before any HTML code is processed by the browser. The most logical place to put this function, because of this requirement, is at the very top of the page.
session_start() allows you to create and use session variables in the page.
Session variables are created by simply assigning a value to the $_SESSION associative array, like this:
```
$_SESSION["fakeLogin"] = "success";
```
The header( ) function allows you to tell the PHP processor to load another (meaning, different) Web page. This action is usually called "redirection". The single argument to header( ) is the string "Location: " concatenated to an absolute URL.
The built-in server variable $_SERVER['HTTP_HOST'] contains the name of the Web server. In this class, the name of the Web server is www.multimedia.richlandcollege.edu or www.mmlab2.rlc.dcccd.edu, depending on where the page is being hosted from.

ADDITIONAL NOTE: For future use, if you have any PHP code after the call to header() for a redirect to another page, you should call exit() after the call to header(). The exit() function tells the PHP processor to stop processing the PHP code in your page. If you don't call exit(), the PHP processor will continue to process your PHP code that is after the call to header(), and you may experience unexpected results.

Richland College Multimedia Learning Center

More Arrays, Strings, and Session Variables

Associative Arrays

foreach Loops

Built-in Associative Arrays

String Functions

Session Variables