奇怪的PHP行为与数字

Question

I am running this code snippet in php.

for ($zip=01001;$zip<99950;$zip++){
// DO WORK WITH MYSQL
    sleep(0.04);    
    echo $zip;
}

To my surprise 513 is the first number that gets echoed, 514 the second and so on. What is going on here?

Answer 1

Convert it to a zero-padded string:

for ($zip=1001; $zip<99950; $zip++){
    $zip = sprintf("%05d", $zip);
    // $zip is now a string ranging from "01001" to "99949"
}