Question

I got the solution; however, I feel like the code is pretty awful. This is within my first 50 hours using any programming language…please bear with me.

The Problem:

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:
1, 2, 3, 5, 8, 13, 21, 34, 55, 89, …
By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.

My Solution:

<?php

//if number is odd, returns false
function setOddsZero($n) {
    $test = ($n&1); //0 = even, 1 = odd
    if($test == 1) {
        return false;
    } else {
        $n = $n;
    }
}


$numbers=array(1,);
for($i>0; $i<=100; $i++) {
$numbers[$i] += (($numbers[$i-2])+($numbers[$i-1]));
  if (($numbers[$i]) >= 4000000) {
      echo $total;
      die;
  } else {
      if((setOddsZero($numbers[$i]))===false) {
          $total += 0;
      }else {
          $total += $numbers[$i];
      }
  }
}
?>

Answer 1

$fibos = array(1,2);
$sum_of_evens = 0;

while ($fibos[1] < 4000000)
{
    $fibos []= array_shift($fibos) + $fibos[0];
    $sum_of_evens += ($fibos[1] & 1 == 0) ? $fibos[1] : 0;
}

echo $sum_of_evens;

---

Less stack-pushy-shify (and thus more efficient) approach, as suggested by meze:

$prevprev = 1;
$prev = 2;
$sum_of_evens = 0;

while ($prev < 4000000)
{
    list($prevprev, $prev) = array($prev, ($prevprev + $prev));
    $sum_of_evens += ($prev & 1 == 0) ? $prev : 0;
}

---

Edit: Modified the code to use & 1 instead of % 2, cf. this thread at devshed.