C++ solution to Project Euler Problem 2

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.

Running time: Unknown

Assessment: Inelegant.

This took me an embarrassingly long time to get right. With the exception of Problem 1, I hadn’t written any code in a few years. As noted before, I hadn’t started measuring execution time yet, so I’m not sure how long it took to run, but it’s basically instantaneous.

```
#include <iostream>
```
```
using namespace std;
```
```
 
```
```
int main()
```
```
{
```
```
	int total = 0;
```
```
 
```

	//3 variables to create the Fibonacci sequence from 1 to X

```
	int one = 1;
```
```
	int two = 2;
```
```
	int three = 0;
```
```
 
```
```
	while (two <= 4000000)
```
```
	{
```
```
		three = one + two;
```
```
		if (two % 2 == 0)
```
```
			total += two;
```
```
		one = two;
```
```
		two = three;
```
```
	}
```
```
 
```
```
	cout << total;
```
```
 
```
```
	return 0;
```
```
}
```

3 thoughts on “C++ solution to Project Euler Problem 2”

Thankyou for this. I was trying to make a vector and sum each number in the vector! I couldn’t achieve this method, too advanced, when the answer was so simple with an if statement! Thanks!

why is the while loop only upto 4000000

I did it slightly differently, my version used only two variables:
a += b;
b += a;
if (a % 2 == 0){ total += a;}
if (b % 2 == 0){total += b;}

this is what was in my while loop, I think yours is a little more elegant though, I am a beginner and I love seeing people write the same solution more efficiently, it is always a learning experience
Thanks!

rianjs.net

Notes for my future self

C++ solution to Project Euler Problem 2

3 thoughts on “C++ solution to Project Euler Problem 2”

Leave a Reply