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Generating Unique Random Numbers Using WHILE Loops - PHP

Do you want to learn how to handle PHP WHILE loops? WHILE loops are one of the most powerful features as well as the easiest loop available to any PHP/MySQL developer. They enable us to shorten repetitive tasks for a highly useful application. This tutorial gives examples of WHILE loops in PHP/MySQL that beginner and novice developers can use as a quick reference for building similar loops in their applications.

TABLE OF CONTENTS:
  1. Mastering WHILE Loops for PHP and MySQL
  2. Using WHILE Loops as Counters
  3. Generating Unique Random Numbers Using WHILE Loops
  4. Constructing Trigonometric Tables Using WHILE Loops
  5. Retrieving All Rows in a MySQL Table Using WHILE Loops
By: Codex-M
Rating: starstarstarstarstar / 9
October 27, 2009

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The above example will not generate unique random numbers. We can still make use of PHP WHILE loops as a counter. But to generate X amount of unique random numbers, we will make use of a PHP array.

A full discussion of arrays is out of the scope of this article. However, below you will find some good references: 

http://www.phphelps.com/7_Creating_and_looping_array_in_PHP.shtml

http://free.netartmedia.net/PHP/PHP50.html

http://www.homeandlearn.co.uk/php/php6p2.html

The strategy is to generate a random number and store it in an array. Then we'll let PHP decide whether or not the generated random number is already stored in the array. If it is stored already, it will not be assigned to the array variable, but will generate a random number again. This will ensure that all values stored in an array are unique.

After the counter reaches its maximum, PHP will then output all the unique values stored in the array using another WHILE looping statement. Below is the example PHP script that will generate 30 unique (non-repetitive) random numbers between 10 and 50:

<?php

//create array

$randomarray = array();

//initiate counter

$i=1;

while ($i<=30) {

//generate random number

$randomnumber = mt_rand(10, 50);

//check first if generated random number is in array if not store it to the array

if(!(in_array($randomnumber,$randomarray))){

//number is not in array, store the number in array and increment counter

$randomarray[]=$randomnumber;

$i++;

}

}

//echo all results inside the array

while (list($key,$value) = each($randomarray)) {

echo $value;

echo '<br />';

}

?>



 
 
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