Conditional cin giving stacked cout messages - c++

Question

Using C++ (g++-4.7 on Mint 16).
Code is a unrefined (and unfinished) Tic-Tac-Toe game.
#include <iostream>
using namespace std;
int main()
{
//initial data
char turn='A';
char ttt[] = {'1','2','3','4','5','6','7','8','9'};
int move;
int over=0; //0 is no, 1 is yes
int valid=0;
while ( over == 0)
{
//display
cout << "\n" << ttt[0] << "|" << ttt[1] << "|" << ttt[2] <<"\n-----\n";
cout << ttt[3] << "|" << ttt[4] << "|" << ttt[5] <<"\n-----\n";
cout << ttt[6] << "|" << ttt[7] << "|" << ttt[8] <<"\n\n Choose a number (Player " << turn << "):";
//ask enter for play with turn
cin >> move;
cout << "\n";
valid = 0;
while (valid == 0)
{
//check if input is valid
if (((move > 0) and (move < 10)) and
((ttt[move-1] != 'A') and (ttt[move-1] != 'B')) and
(cin))
{
ttt[move-1] = turn;
valid=1;
}
else
{
cout << "Invalid slot. Choose a number (Player " << turn << "):";
cin >> move;
cout << "\n";
}
}
//check if done if no //change turn then goto //display
if (((ttt[0]==ttt[1]) and (ttt[1]==ttt[2])) or
((ttt[3]==ttt[4]) and (ttt[4]==ttt[5])) or
((ttt[6]==ttt[7]) and (ttt[7]==ttt[8])) or
((ttt[0]==ttt[3]) and (ttt[3]==ttt[6])) or
((ttt[1]==ttt[4]) and (ttt[4]==ttt[7])) or
((ttt[2]==ttt[5]) and (ttt[5]==ttt[8])) or
((ttt[0]==ttt[4]) and (ttt[4]==ttt[8]))or
((ttt[2]==ttt[4]) and (ttt[4]==ttt[6])))
{
//display winner or say draw
cout << "Player " << turn << " wins!\n";
over=1;
}
else
{
//change turn
if (turn=='A')
{ turn='B';
}
else
{ turn='A';
}
}
}
return 0;
}
There seem to be a bug on the code. On the part where check if input is valid the and (cin) seem to be failing.
When entering a character, (Instead of a number) it output continuously stacks of:
Invalid slot. Choose a number (Player A or B):
I tested the rest of condition without it, it was all working well. Is there a problem on the code or is this really "cin" problem? I've also tried out !(!cin) but it's the same scenario.

Answer 1

You must clear the fail bit from the cin stream in your else block.
When you enter a character that isn't an integer, the cin stream sets the fail bit, which you correctly check for in your if statement, but you never clear it afterward. This causes your input validity check to be false forever.
#include <limits>
...
else
{
cin.clear(); // Add this line
cin.ignore(numeric_limits<streamsize>::max(), '\n'); // And this one
cout << "Invalid slot. Choose a number (Player " << turn << "):";
cin >> move;
cout << "\n";
}
For additional information, see the documentation for std::basic_ios::clear
Update: see this question and this question for similar problems.
Essentially, you also need to tell cin to ignore whatever is in the stream or it will continually set the fail bit with its bad contents you haven't cleared yet. I modified the above snippet to work.