fib_C.c

#include <stdio.h>

int main ()
{
    int a = 0, b = 1, c = 1, sum = 0;

    while (c < 4000000)
    {
        if (c % 2 == 0)
            sum += c;

        c = a + b;
        a = b;
        b = c;
    }

    printf("%d\n", sum);

    return 0;
}