Poking fun at how recursion is taught as the holy grail of CS in entry-level courses.

forkonacci.c

/**
 * Poking fun at how recursion is taught as the holy grail in entry-level CS.
 * This forks a process for each recursive computation and uses the return
 * status as the return value.
 *
 * Running this might be a really bad idea!
 */

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

int main(int argc, const char *argv[]) {
	int n = atoi(argv[1]);
	
	if (n == 0) {
		if (argc == 2) {
			printf("0\n");
		}
		exit(0);
	} else if (n == 1) {
		if (argc == 2) {
			printf("1\n");
		}
		exit(1);
	}

	int v1, v2;
	pid_t p1, p2;
	char n1[10], n2[10];

	if ((p1 = fork()) == 0) {
		sprintf(n1, "%d", n-1);
		char *args1[4] = {"a.out", (char *) n1, "noprint", NULL};

		execv("a.out", args1);
	} else if (p1 < 0) {
		printf("ERROR\n");
	}

	if ((p2 = fork()) == 0) {
		sprintf(n2, "%d", n-2);
		char *args2[4] = {"a.out", (char *) n2, "noprint", NULL};

		execv("a.out", args2);
	} else if (p2 < 0) {
		printf("ERROR\n");
	}

	waitpid(p1, &v1, 0);
	v1 = WEXITSTATUS(v1);
	waitpid(p2, &v2, 0);
	v2 = WEXITSTATUS(v2);
	
	if (argc == 2) {
		printf("%d\n", v1 + v2);
	}

	exit(v1 + v2);
}