为什么我的PHP while（）里面的while（）没有上升？

I'm using this simple while loops inside of a while loop and whats happening is the $x is working how i planned but the $i isnt.

$i = 0;
$x = 0;

while ($i <= 50) {
    while ($x <= 50) {
        echo $i . $x . "<BR/>";
        $x++;
    }
    $i++;
}

I'm getting the response;

00
01
0...
050

but then the script is stopping? $i isn't incrementing and running the while loop 50 more times so i would have

00
01
0...
050
10
11
1...
150

The problem is that you have to initialize $x to 0 at the beginning of the outer while loop. Your $x variable will never enter the inner while loop because $x is already greater than 50

$i = 0;

while ($i <= 50) {
    $x = 0;
    while ($x <= 50) {
        echo $i . $x . "<BR/>";
        $x++;
    }
    $i++;
}