1) 

x = 1, y = 0
x = 0, y = -1
x = -1, y = -2
infinite


2) 
***4***
1 2 3 
***3***
1 2 

3) 

#include <stdio.h>

main(){
	int product=1, valread;

	scanf("%d",&valread);
	while (valread != 0){
		product *= valread;
		scanf("%d",&valread);
	}	
	return 0;
}