Can't quite get Project Euler problem #2 figured out

c++

Solution

You're using `y` as both the loop variable, and the second term in the sequence.

What you mean to do is:

int x = 0;
int y = 1;
int z;
int sum = 0;

do {
    z = x + y;
    x = y;
    y = z;
    if (y % 2 == 0) sum += y;
} while (y <= 4000000);

Noting that you should probably initialize `sum` as well.

Problem

I'm trying to learn the basics of C++ by going through some Project Euler problems. I've made it to...#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, ... Find the sum of all the even-valued terms in the sequence which do not exceed four million. My logic: ``` 0, 1, 1, 2, 3, 5 x y z x y z x y z x y z ``` The above is looping through this: ``` x + y = z x = y y = z ``` My code: ``` #include <iostream.h> using namespace std; int main() { int x = 0; int y = 1; int z; int sum; for(y = 1; y <= 4000000; y++) { z = x + y; x = y; y = z; if(y % 2 == 0) { sum += y; } } cout << sum; cin.get(); } ``` That outputs `4613788` The correct answer, though, is `4613732`.

Original source