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PHP Coding Tests: Find All Prime Numbers Up to 100

Yet another coding test and another fail-boat by me! I tried to rack my brain around this one but my on-the-spot math skills are limited. I don't know why I blank on these during the process, but I was given time on my own to figure it out. I took that opportunity, even if it doesn't mean the job, to make sure I can do basic math.

You can insert any number to find the prime number to, but in this case, we're doing 100.

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// total number to loop through
$total = 100;
// 1 is always prime and its weird so here it is
echo 1 . "\n";
// loop through the total number provided to go through
for($i = 2; $i <= $total; $i++) {
  // loop through each number up to the number we are currently going through
  // ie. if its 4, we want to loop through 2, 3, 4
  // skipping 1 because everything is divisible by 1
  for($j = 2; $j <= $i; $j++) {
    // if the current number matches the counted up number
    // we've hit the end and can consider this prime
    if($i == $j) {
      echo $i . "\n";
    }
    // checks each number using modulo
    // ie. if there is NOT a remainder, then this isnt prime
    if($i % $j == 0) {
      break;
    }
  }
}

Comments spell it out above. Let me know what you think!

Categories: Development

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