Arithmetic-Derivative/arithmetic_derivative.c

#define VERSION "0.10"
#define N 100

#include <stdio.h>

int derive (int n);
void split (int value, int *a, int *b);

int main () {
	int n, res;
	int sgn;
	char again;
	do {
		sgn = 1;
		printf ("Enter an integer: ");
		scanf ("%d", &n);
		if (n < 0)
			sgn = -1;
		res = derive (sgn * n);
		res = sgn * res;
		printf ("The arithmetic derivative of %d is: %d", n, res);
		getchar ();
		printf ("\nAgain? [y/n] ");
		scanf ("%c", &again);
	} while (again != 'n');
	printf ("\n\n\nversion: %s", VERSION);
}

int derive (int n){
	int a = 1, b = 1;
	switch (n) {
		case 0:	return 1; break;
		case 1: return 0; break;
		default:
			split (n, &a, &b);
			if (b > 1){ // not a prime
				n = derive (a) * b + a * derive (b);
			} else {
				n = 1;
			}
			return n; 
			break;
	}
}

void split (int value, int *a, int *b) {
	int i = 2;
	int j = 0;
	do {
        if (value % i == 0) {
			*a = i;
			*b = value / *a;
			j++;
		}
		i++;
	} while (j == 0);
}