Why code goes to infinite loop? (

Question

<?php
$mines = 10;

####
for($x=1; $x<=9; $x++) {
    for($y=1; $y<=9; $y++) {
        $minefield[$x][$y] = 0;
    }
}       

for($i=0; $i<$mines; $i++) {
    $randx = rand(1, 9);
    $randy = rand(1, 9);

    if($minefield[$randx][$randy] == 'X') {
        $i--;
    } else {
        $minefield[$randx][$randy] = 'X';
    }
}

What's i doing wrong?

Answer 1

When comparing strings (or resources) with integers, strings are translated to numbers first, as per the documentation , then compared.

As such, this:

if ($minefield[$randx][$randy] == 'X')

... where $minefield[$randx][$randy] = 0 is equivalent to:

if (0 == 0) // 0 == (int)'X'

... which is always true. Therefore, you are incrementing and decrementing $i at each iteration.

Answer 2

I would try to set the $minefield[$x][$y] = '0'; with the quotes, so that both types are string. Might be an issue with that.

Check out the PHP Manual on this subject Comparing Strings to Numbers

Answer 3

as a guideline I would not do $i-- inside the loop, as this is a classic infinite-loop generator. instead do another loop inside that keep on generating random mines until it doesn't hit an existing one.

Answer 4

There is another solution to your problem. You can set it like that and be sure you pick only 10 positions in limited set of coordinates:

<?php

// build minefield
$minefield = array();
for($x=1; $x<=9; $x++) {
    $minefield[$x] = array();
    for($y=1; $y<=9; $y++) {
        $minefield[$x][$y] = 0;
    }
}

// prepare cartesian func
function array_cartesian() {
    $_ = func_get_args();
    if(count($_) == 0)
        return array(array());
    $a = array_shift($_);
    $c = call_user_func_array(__FUNCTION__, $_);
    $r = array();
    foreach($a as $v)
        foreach($c as $p)
            $r[] = array_merge(array($v), $p);
    return $r;
}

// get coordinates
$coords = array_cartesian(range(1,9), range(1,9));
// pick random coordinates' keys
$chosen_coords = array_rand($coords, 10);

foreach ($chosen_coords as $key) {
    $minefield[$coords[$key][0]][$coords[$key][1]] = 'X';
}

I know, it is lengthy, but I could write it in 2-3 lines in Python.

Ps. The code for cartesian product is from here: https://stackoverflow.com/a/2516779/548696

Answer 5

the problem is in your second loop. as the indexes are random numbers, so maybe array value of these indexes has been set to X in the else statement, and by a random chance, same indexes will be checked again and again so it will goes to if statement and here is where you minus i !

It is not a good practice to change the value of loop variable i in the body of the loop.

Answer 6

obviously because you decrement the loop counter:

if($minefield[$randx][$randy] == 'X') {
    $i--;
} else {
    $minefield[$randx][$randy] = 'X';
}

at one point all fields will equal 'X' and you'll have an infinite loop.

it is a very bad habit to play with the index in a for loop