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Problem 2: Even Fibonacci Numbers

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.

Solution

/*
 * Even Fibonacci numbers
 * Problem 2 <https://projecteuler.net/problem=2>
 *
 * Project Euler
 *
 * By Ankit R Gadiya
 */

#include <stdio.h>

int main (void)
{
	unsigned long long int sum = 0, num1 = 1, num2 = 1, num3;

	do {
		num3 = num1 + num2;

		if (num3 % 2 == 0)
		sum += num3;

		num1 = num2;
		num2 = num3;
	} while (num3 < 4000000);

	printf("Sum: %lld\n", sum);

	return 0;
}

prob2.c

Result

4613732