第三题

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

typedef struct node
{
	int         data;
	struct node * next;
} NODE;
int num[1000000];
void output(NODE *);
void change(int n, int m, NODE *head) {
	int flag;
	
	NODE *r = head;
	int a, b;
	NODE *ss = (NODE *)malloc(sizeof(NODE));
	a = n * 10 / m;
	b = n * 10 % m;
	ss->data = a;
	head->next = ss;
	r = head->next;
	a = b;
	num[n]++;
	
	while (a > 0)
	{
	
		if (num[a]== 0)
		{
			num[a]++;

			NODE *p = (NODE *)malloc(sizeof(NODE));
			p->data = a*10/m;
			b = a * 10 % m;
			r->next =p;
			r = p;
			a = b;
		}
		else if (num[a] != 0)
		{
			b = a * 10 /m;
			NODE *p = head;
			while (p->data != b)
			{
				p = p->next;
			}
			r->next = p;
			break;
		}
	}
	if (a == 0)
	{
		r->next = NULL;
	}

};

void output(NODE * head)
{
	int k = 0;

	printf("0.");
	while (head->next != NULL && k<50)
	{
		printf("%d", head->next->data);
		head = head->next;
		k++;
	}
	printf("\n");
}

int main()
{
	int n, m;
	NODE * head;

	scanf_s("%d,%d", &n, &m);
	head = (NODE *)malloc(sizeof(NODE));
	head->next = NULL;
	head->data = -1;
	change(n, m, head);
	output(head);

	return 0;
}