array_flip($input)

$input represents the array to flip, and when executed, array_flip() returns the new (flipped) array.

Finally, take a look at your first search function in PHPthe in_array() function. This function takes two parameters (the value being searched for and the array to search) and returns a Boolean value indicating whether the particular value was found as described in the syntax that follows:

in_array($needle, $haystack [, $strict])

Note that the in_array() function also provides a third optional parameter, $strict. This optional Boolean value (false by default) determines whether the value specified in the $needle parameter must match not only the value, but the data type found in the corresponding array, $haystack. Thus, in an array with the string value 10, searching for the integer value 10 would return true. However, by setting the $strict parameter to true the same operation would return false.

Now that you have been introduced to the new functions being used in this example, let's take a look at the first portion of the cryptogram script, as shown in :

Listing 2.17. A Cryptogram Generator Using PHP Arrays (Part 1)

<?php

    /* Initialize the random number generator */
    srand((double)microtime() * 1000000);

    $message = "This is my super secret message!";
    $message = strtoupper($message);

    /* Create an alphabet array whose keys are the letters A-Z, and whose
       values are the numbers 0 - 25 respectively */
    $alphabet = array_flip(range('A', 'Z'));
    $cryptogram = range('A', 'Z');

    /* Randomize the lookup table used for the cryptogram generation */
    shuffle($cryptogram);

As shown in , the first step in your cryptogram script is the initialization of the random-number generator. As was the case with array_rand(), the shuffle() function requires this to function properly. The $message variable (which represents the actual string you are encoding) is then initialized and converted to uppercase using the strtoupper() function. Using a combination of the range() function coupled with the array_flip() function, we create an associative array, $alphabet, which has key values for every letter in the alphabet and associates these values with the integers 0 tHRough 25. Complementing the $alphabet variable is the $cryptogram variable, which is initialized with 26 values representing the letters of the alphabet. The $cryptogram variable will be used to encode the message into the final cryptogram.

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