# Duncan's blog

## September 20, 2014

### Project Euler: problem 2 (PHP) – Even Fibonacci numbers

Filed under: PHP,Project Euler — duncan @ 8:00 am

I previously blogged about this Project Euler puzzle 6 years ago, using ColdFusion.  This is my approach using PHP as a simple practical exercise for myself, and I’d appreciate any feedback on my PHP code.

Project Euler problem 2:

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.

A minor clarification in the specification from when I did this last.

```<?php
\$sum = 0;
\$fibonacci = 1;
\$old1 = 0;
\$old2 = 1;

while (\$fibonacci <= 4000000) {
\$fibonacci = \$old1 + \$old2;
\$old1 = \$old2;
\$old2 = \$fibonacci;

if (\$fibonacci % 2 == 0) {
// it's an even number
\$sum += \$fibonacci;
}
}

echo \$sum;
```

Be sure and read my friend and colleague Adam Cameron’s blog article about another way to do the Fibonacci sequence in PHP using generators.