C :

#include <stdio.h>
int main()
{
	int a,b,n,c,num,d;
	while(scanf("%d%d%d",&a,&b,&n)!=EOF)
	{
		num=0;
		c=a%b;
		while(1)
		{
			c=c*10;
			d=c/b;
			c=c%b;
			if(c==0)
			break;
			num++;
			if(num==n)
			break;
		}
		if(num==n)
		printf("%d\n",d);
		else
		printf("0\n");
	}
	return 0;
}

C++ :

#include <bits/stdc++.h>
using namespace std;
int d[1000005];
int visited[1000005];
int main()
{
	int a,b,n;
	while(~scanf("%d%d%d",&a,&b,&n)){
		memset(visited,0,sizeof(visited));
		memset(d,0,sizeof(d));
		int len=0;
		a=a%b;
		int flag=0;
		while(a>0&&len<n){
			if (visited[a]){
				flag=1;
				break;
			}
			visited[a]=1;
			a=a*10;
			d[len++]=a/b;
			a=a%b;
		}
		
		if (len==0){
			printf("0\n");
			continue;
		}
		
		n--;
		if (flag) n=n%len;
		printf("%d\n",d[n]);
	}
	return 0;
}