Euler2

Euler2.c

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

int sum_even_fibonacci(int limit, int *steps_taken) {
    int a = 1, b = 0;
    int sum = 0;
	int even_fibonacci = 0;
    for (int steps = 1; even_fibonacci < limit; steps++) {
        assert(a % 2);        // Fibonacci just before even Fibonacci
        assert(b % 2 == 0);   // Even Fibonacci

		sum += even_fibonacci;
        even_fibonacci = 2 * a + 3 * b;
        a += 2 * b;
        b = even_fibonacci;

        if (steps_taken) *steps_taken = steps;
    }
    return sum;
}

int main(int argc, char ** argv){

	if(argc!=2){
		printf("Invalid number of arguments\n");
		printf("Usage a.exe [limit]\n");
		return EXIT_FAILURE;
	}

	int limit = atoi(argv[1]);

	if(limit < 3){
		printf("Invalid input\n");
		printf("Enter a limit of 3 or more\n");
		return EXIT_FAILURE;		
	}

	int steps_taken = -1;
	int sum = sum_even_fibonacci(limit,&steps_taken);

    printf("Sum of the even-valued fibbonaci below %d\n",limit);
    printf("Answer = %d, Steps Taken = %d\n",sum,steps_taken);

	return 0;
}