Thread: ****.exe has stopped working

I wrote a code below to find out the prime factors using recursion. it runs fine but terminates with a message: primfactor.exe has stopped working. check for online solution.. any idea why so?

Code:

/*prime factor by recursion*/
#include<stdio.h>
int rec (int,int); /* this semi colon is must*/
int main(void)
{
	int n;
	printf("Enter any positive integer for prime factorization ? ");
	scanf("%d",&n);
	rec(n,2);
	return (0);
}
int rec(int n, int l)
{
	
	while (1)
		{
			if (n%l==0)
			{
				printf("%d ",l);
				n=n/l;
			}
			else
			{
				if (n==l)
					break;
				rec(n,l+1);
			}
		}
	return (0);
}

You are thinking iteratively, not recursively.

The number of times you recursively call the function doesn't need to be known. What needs to be known is:

1) that you have in fact a stopping point for the recursion. It's essential that the recursion not go horribly deep with nested calls.

2) that you are calling the function with the right parameters. Generally, some progress must be made, with each execution through the recursive function.

so what you think must be the right recursive solution for this problem? shall I replace the while loop with another recursive call to says rec1?

thinking more recursively, I changed the while(1) loop into another recursive call:

Code:

/*prime factor by recursion*/
#include<stdio.h>
int rec (int,int);
int rec1 (int, int); /* this semi colon is must*/
int main(void)
{
	int n;
	printf("Enter any positive integer for prime factorization ? ");
	scanf("%d",&n);
	rec(n,2);
	return (0);
}
int rec(int n, int l)
{
	n=rec1(n,l);
	if (n>l)
		rec(n,l+1);
	return 0;
}
int rec1(int n, int l)
{
	if (n%l==0)
	{
		printf("%d ",l);
		n=n/l;
		rec1(n,l);
	}
	return n;
	return 0;
}

But the code is wrong answer for n=288

any help possible?

you are right.. I finally found a pure recursive solution with just one recursive function.

Code:

/*prime factor by recursion*/
#include<stdio.h>
int rec (int,int); /* this semi colon is must*/
int main(void)
{
	int n;
	printf("Enter any positive integer for prime factorization ? ");
	scanf("%d",&n);
	rec(n,2);
	return (0);
}
int rec (int n, int l)
{
	if (n%l==0)
	{
		printf("%d ",l);
		n=n/l;
		rec(n,l);
	}
	else
	{
		if (n<l)
			return 0;
		else
		{
			l=l+1;
			rec(n,l);
		}
	}
	return 0;
}

for learning purpose, How could we possibly use an recursive call from master recursive call? would be interesting to know..

I found this code working fine. it uses another recursive call from a recursive call.. I don't know if calling them master-slave is valid or not.. but it is good learning about recursive functions and calling them from each other..

Code:

/*prime factor by recursion*/
/* calling another recursive function from a recursive function*/
#include<stdio.h>
int rec (int,int);
int rec1 (int,int);
int main(void)
{
	int n;
	printf("Enter any positive integer for prime factorization ? ");
	scanf("%d",&n);
	rec(n,2);
	return (0);
}
int rec(int n, int l)
{
	int x;
	x=rec1(n,l);
	l=l+1;
	if (x>=l)
		rec(x,l);
	else
		return (0);

}
int rec1(int n, int l)
{
	if (n%l!=0)
		return (n);
	else
	{
		printf("%d ",l);
		n=n/l;
		rec1(n,l);
	}
}