Generating a Non-Repeating Random Number - PHP - php

Question

I'm trying to get a custom function in php to return a random number between 1 and 20 that does not repeat i.e. produce the same number more than once, since I need to subsequently use this number to navigate to one of twenty web pages, and I don't want the same web page displayed.
Here is my code in three steps:
<form action="rand.php">
<p>Click this button to display a random number that does not repeat...</p>
<p><input type="submit" value="Generate"></p>
</form>
Here is rand.php:
require_once('functions.php');
$page = generateNumber();
echo $page;
Here is functions.php:
<?php
$check = array();
function generateNumber() {
global $check;
$page_no = mt_rand(1,20);
$check[] = $page_no;
if (count($check) != 1) {
foreach ($check as $val) {
if ($val == $page_no) {
$page_no = mt_rand(1,10);
continue;
}
}
return $page_no;
}
else {
return $page_no;
}
}
?>
My code seem to be functioning, however, it is repeating numbers so I am obviously doing something wrong. The reason I initially check the count is so that is returns the first number regardless, since it would be a single fresh number.
In order to see the number change I have been refreshing the rand.php page in my browser.

Answer 1

I would keep it simple.
// List numbers 1 to 20
$pages = range(1,20);
// Shuffle numbers
shuffle($pages);
// Get a page
$page = array_shift($pages);

Answer 2

In order to go through all the 20 numbers on each page visit, without repeating, you will need to set a session variable.
<?php
session_start();
if (!isset($_SESSION['numbers'])) {
$_SESSION['numbers']="*"; //---create the session variable
}
function get_number() {
$i = 0;
do {
$num=rand(1,20); //---generate a random number
if (!strstr($_SESSION['numbers'],"*".$num."*")) { //---check if the number has already been used
$_SESSION['numbers']=$_SESSION['numbers'] . $i . "*"; //---add the number to the session variable to avoid repeating
if (substr_count($_SESSION['numbers'],"*")>=21) { //---resets the session variable when all 20 number have been used
$_SESSION['numbers']="*";
}
$i=$num; //---ends the while loop to return the value
}
} while ($i==0);
return $i;
}
?>