Project Euler - Problem 2 Solution With PHP

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.

Our second problem gives us a sequence which our teachers forced us to learn at the primary school. The lovely "Fibonacci sequence".

Here is an option to solve this problem in PHP:

``````\$n1 = 1;
\$n2 = 2;
\$n3 = \$n1 + \$n2;

\$sum = 2;

while (\$n3 < 4000000) {
\$n1 = \$n2;
\$n2 = \$n3;
\$n3 = \$n1 + \$n2;

if (\$n3 % 2 == 0) {
\$sum += \$n3;
}
}

echo \$sum;
``````

We already know the first three numbers which create us a pretty nice start point for our tiny calculator. So we define the first three numbers and according to our "hard-coded" data, we define the `\$sum`. The important point is to keep in mind that only the even numbers should be added to the `\$sum`.

In the `while` loop, we check if the next number of the sequence smaller than 4 million. If it is, we are good to go and check if our second condition passes.

We know that the `modulus` (`%`) of even numbers to `2` should result `0`. So we write out `if` statement and all done!

Execution time: 0s