Terminating loop properly?

Hmm need some help trying to terminate the loop. Basically I want to receive a set of 2 integers, so when the user wants to terminate he/she should just enter nothing and press another enter.

So for example, input would be:
5 50
7 70
<enter> (this should terminate the input process and it should process the data)

Any input would be appreciated - my C may be a bit rusty since I haven't coded in a while so bare with it
Here's what I got so far:

Code:

/* The 3n+1 Problem */

#include <stdio.h>

/* Gets the cycle length for an input n */
int get_cycle_length(int n);
/* Returns the maximum cycle length between i and j */
int maximum_cycle_length(int i, int j);
struct node* insert_data(struct node**, int, int);
void print_list(struct node*);

/* Structure for storing info */
struct node {
	int i;
	int j;
	int result;
	struct node *next;
};

int main(int argc, char **argv)
{
	int i, j, k=0, res=0;
	int max_cycle = 0;
	struct node* empty = NULL;
	
	while(1){
		if (scanf("%d %d",&i, &j) != 2)
		{
			/* Checking Exceptions here */
                        /* Need help here!! */
			if ((k = getchar()) == '\n')
				break;
			break;
		} else
		{
			insert_data(&empty,i,j);
		}			
	}
	print_list(empty);	
	printf("\n");

	return 0;
}

int get_cycle_length(int n)
{
	int cycles = 0;
	/* Implement algorithm */
	while (n != 1)
	{
		if (n % 2 == 0){
			n /= 2;
		} else {
			n = 3*n + 1;
		}
	cycles++;
	}
	cycles++; 
	return cycles;
	
}

int maximum_cycle_length(int i, int j)
{
	int k, res, max_cycle = 0;

	for (k = i; k <= j; k++)
	{
		res = get_cycle_length(k);
		if (res >= max_cycle)
			max_cycle = res;
	}

	return max_cycle;
}

struct node* insert_data(struct node** list, int i, int j)
{
	if (*list == NULL)
	{
		*list = malloc(sizeof(struct node));
		(*list)->i = i;
		(*list)->j = j;
		(*list)->result = maximum_cycle_length(i,j);
		(*list)->next = NULL;
	}
	else
	{
		/* Traverse until reach insertion point */
	struct node* current = *list;
	while (current->next != NULL)
	{
		current = current->next;
	}
	struct node *new = (struct node*)malloc(sizeof(struct node));
	new->i = i;
	new->j = j;
	new->result = maximum_cycle_length(i, j);
	new->next = NULL;
	current->next = new;
	}	
		/* Finish up by returning head */
	return *list;
}

void print_list(struct node* list)
{
	if (list == NULL)
	{
		printf("Empty list - nothing printed\n");
		return;
	} else {
		while (list != NULL){
		printf("%d %d %d",list->i, list->j, list->result);
		printf("\n");
		list = list->next;
		}	
	}
	return;
}

how about using fgets/sscanf combination for input instead of scanf. then if sscanf does not return 2 break the loop.