Fun guessing game (not binary search! Four digits)

  The following is the four digit guessing game code ：

#include <bits/stdc++.h>
#include <windows.h>
#include <stdio.h>
#include <cstdlib>
#include <iostream>
#include <conio.h>
#include <time.h>
#include <ctime>
using namespace std;
int main()
{
	srand (time(0));
	time_t t1;
	int n1,n2,n3,n4;
	int a1,a2,a3,a4;
	int a,s1,s2;
	cout <<" A four digit number with different digits  N , It depends on how long it takes you to guess .\n\n";
	cout <<"            ";
	system ("pause");
	system ("cls");
	cout <<" A four digit number with different digits  N , It depends on how long it takes you to guess .\n\n";
	time(&t1);
	t1=t1+1;
	n1=rand()%9+1;
	do
		n2=rand()%10;
	while (n1==n2); 
	do
		n3=rand()%10;
	while (n1==n3 || n2==n3);
	do
		n4=rand()%10;
	while (n1==n4 || n2==n3 || n3==n4);
	while (1)
	{
		s1=0;s2=0;
		cin >>a; 
		a1=a/1000;
		a2=a/100%10;
		a3=a/10%10;
		a4=a%10;
		if (a1==0 || a1>9)
		{
			cout <<" Does not meet the four digit requirement .\n\n";
			Sleep(500);
			continue;
		}
		if (a1==a2||a1==a3||a1==a4||a2==a3||a2==a4||a3==a4)
		{
			cout <<" It does not meet the requirements of different digits .\n\n";
			Sleep(500);
			continue;
		}
		if (a1==n1||a1==n2||a1==n3||a1==n4)
		{ 
			if (a1==n1)
			{
				s1++;
				s2++;
			}
			else
				s1++;
		} 
		if (a2==n1||a2==n2||a2==n3||a2==n4)
		{ 
			if (a2==n2)
			{
				s1++;
				s2++;
			}
			else
				s1++;
		}	
		if (a3==n1||a3==n2||a3==n3||a3==n4)
		{ 
			if (a3==n3)
			{
				s1++;
				s2++;
			}
			else
				s1++;
		}
		if (a4==n1||a4==n2||a4==n3||a4==n4)
		{ 
			if (a3==n3)
			{
				s1++;
				s2++;
			}
			else
				s1++;
		}
		if (s2==4)
		{
			cout <<" You guessed it ！";
			break; 
		}
		else if (s1==0&&s2==0)
			cout <<" None of the digits is right \n";
		else if (s2==0)
			cout <<" You're right  " <<s1 <<"  individual  , The position is not right at all \n";
		else
			cout <<" You're right  " <<s1 <<"  individual  , The position is right " <<s2 <<" individual .\n";
	}
	time_t t2;
	time(&t2);
	Sleep (50);
	system ("cls");
	cout <<" You use the  " <<(t2-t1)/60 <<" minute  " <<(t2-t1)%60 <<" second ";
	return 0; 
}