Random multiplication table generator

im creating an multiplication table system in PHP.

The input tho this system is an table number and the amount of questions. The table 1 is skipped so 2 to input table

At this point I just fill an array like this:

$nCount = $_POST['count'];
$nHighest = $_POST['table'];
$aSums = [];
$nCounter = 0;
while($nCount > 0){
    $cSumString = rand(2, $nHighest) . "*" . rand(1, 10);
    $aSums[$nCounter] = $cSumString
    $nCount--;
    $nCounter++;
}

I want to parse the questions in multiple ways:

3 * 5 = ... (normal)
... * 5 = 25 (first number to fill in)
8 * ... = 16 (second to fill in)

This needs to be randomised.

Example:

1 * 2 = ... 
6 * ... = 12 
... * 4 = 20
8 * 4 = ...
2 * ... = 6

The only thing I know that should be able to so this is a switch but I cant seem to get it to work propperly so if anyone can give me a push in the right direction i would appreciate it. Im not asking for instacode just some tips would be great.

Solution

$nCount = $_POST['count'];
$nHighest = $_POST['table'];
$aSums = [];
$leftOut = ['leftFactor', 'rightFactor', 'product'];

for ($i = 0; $i <= $nCount; $i++) {
  $leftOutRand = rand(0, count($leftOut) - 1);
  $factor = rand(1, $nHighest);
  $product = rand(0, $nHighest) * $factor;
  switch($leftOut[$leftOutRand]) {
    case 'leftFactor':
      $cSumString = '...' . ' * ' . $factor . ' = ' . $product;
      break;
    case 'rightFactor':
      $cSumString = $factor . ' * ' . '...' . ' = ' . $product;
      break;
    case 'product':
      $cSumString = rand(1, $nHighest) . ' * ' . rand(1, $nHighest) . ' = ' . '...';
      break;
  }
  $aSums[$i] = $cSumString;
}

example Output:

2 * ... = 4
... * 2 = 6
1 * 1 = ...
... * 2 = 6
3 * ... = 12
2 * ... = 2
2 * 4 = ...
4 * ... = 0
3 * 1 = ...
2 * 1 = ...
... * 4 = 16
1 * ... = 2
... * 2 = 2
1 * 4 = ...
3 * ... = 9
2 * 3 = ...
2 * ... = 6
... * 1 = 3
... * 4 = 4
1 * 1 = ...
... * 3 = 9