How to move a step back in foreach loop?

How do i move a step back in a foreach loop? Say i have something like this:

Do something for the first run. If b == 1, do something again. See code below.

$i = 0;
foreach ($a as $b) {
  if ($i == 0) {
     //something
  }
开发者_运维技巧  if ($b == '1') {
    $i = 0;
  }
  $i++;
}

The problem is, when $b == 1, it is setting $i = 0 but not running the instructions inside. Any better way to overcome this if it's not possible to step back?

Update: Thanks guys for the response. Sorry i wan't clear when i typed this.

But I'd managed to achieve what i want by putting the loop in a function and do some conditional checks and pass arguments before calling it.

Not sure if this is a typo, but you have if ($i = 0) instead of if ($i == 0). Possibly your problem is there?

Perhaps another option would be just doing:

if ($b == '1') {
    // do something?
}

Final option would be to do a regular for loop and decrement the counter if a condition exists:

for ($x = 0; $x < count($thing); $x++) {
    if($thing[$x] == '1') {
        $x -= 1;
    }
}

are you sure that $i is getting set to 0 in the loop, it is quite possible it is always 0 (because that is what it is set to before the loop)