ex-1.11 SICP in C

gistfile1.c

#include <stdio.h>

/*
f(0) = 0
f(1) = 1
f(2) = 2
f(3) = f(2) + 2f(1) + 3f(0)
     \      \       \
f(4) = f(3) + 2f(2) + 3f(1)
     \      \       \
f(5) = f(4) + 2f(3) + 3f(2)
 */

int main(int argc, char* argv[])
{
	printf("%d\n", func(5));
}

int func(int n) 
{
	int a = 2;
	int b = 1;
	int c = 0;
	int i = 2;

	if (n<3) {
		return n;
	}

	while (i != n) {
		int ta = a + 2*b + 3*c;
		int tb = a;
		int tc = b;

		a = ta;
		b = tb;
		c = tc;

		i++;
	}

	return a;
}