Help with changing array/tic tac toe game

[PadreDoom]

Hi y'all. I'm trying to teach myself C++ for my own personal betterment. I have a little experience with JS and Java, but I'm just diving into C++.

I'm working on a tic tac toe exercise. I am running into a problem where, after I input a grid position, other parts of the array are losing their default '_' character, and sometimes it's saying a position has been taken when I know it's still open.

For example: First round, player 1 input for "1" yields:
x _ _
_ _ _
_ _ _

First round, player 2 input for "5" yields:
The spot has already been taken. Try again.
x _ _
_
_ _ _

I know it says position 5 has been taken because it no longer points to an underscore. But I'm wondering why I'm losing the underscore in the first place. I tried changing the array to a vector, but still had the same issue. If I run the code long enough, I start to get weird smiley-type characters in certain spots on the grid.

I removed some aspects of the code that I think are irrelevant to the problem.

#include <iostream>
//Function setGrid initializes blank grid. Called in main. 
void setGrid ( char grid [] )
{
    for ( int i = 0; i < 9; i++ ) 
	{
		grid[i] = '_';
	}
}

//Function showGrid displays current array, inserting line 
//breaks where needed
void showGrid ( char grid [] )
{
    std::cout << "\n";
    for ( int i = 0; i < 9; i++ )
    {
	if ( i == 3 || i == 6 ) 
	{
	   std::cout << "\n";
	}
        std::cout << grid[i] << " ";
    }
	std::cout << "\n";
} 
//Function playSquare changes an array index to player's character 
//based on input. Called in while loop in main. 
void playSquare ( char grid [], char player, int input )
{
    if ( input < 1 || input > 9 )
		std::cout << "That number doesn't work. Try again: ";
    else if ( grid[input-1] != '_' )
		std::cout << "That spot's been taken. Try again.";
    else
		grid[input-1] = player;
}          

int main() {
           
    char p1x = 'x';
    char p2o = 'o';
    int userInput;
    char gameGrid [9];
                       
    setGrid ( gameGrid );
    showGrid ( gameGrid );
           
    while ( !isOver || counter < 9 )
    {
        std::cout << "Player 1, enter your number: ";
        std::cin >> userInput;
        playSquare ( gameGrid, p1x, userInput );
        showGrid ( gameGrid );
      
        std::cout << "Player 2, enter your number: ";
        std::cin >> userInput;
        playSquare ( gameGrid, p2o, userInput );
        showGrid ( gameGrid );
    };
    std::cout << "Game over.";
    return 0;
}

[Hippogriff]

The reason your code isn't working correctly is because of your winning condition check. For example if you check lines 45-48 you can see several of them use '=' instead of '=='. Meaning they are changing the value instead of comparing them.

 else if ( grid[3] = player && grid[6] == player )
			return true;
  else if ( grid[4] = player && grid[8] == player )
			return true;

Go through all of them and double check that and it should work correctly. Otherwise the code looks fairly well done (would be nice if it told you which player won as well).

[PadreDoom]

Of course. And to think I edited those lines out of my initial post because I thought they were irrelevant. Thank you very much.

[Computergeek01]

I noticed that you don't give either player another chance if they enter an invalid character or try to take an occupied space. You may want to also filter out bad input with "isdigit()": http://www.cplusplus.com/reference/clibrary/cctype/isdigit/

[PadreDoom]

Hi CG,

Good call on that fault in logic, and on the isdigit suggestion. This is how I implemented it (in the main, I changed userInput to a type of character array initialized to size 100). If you have any suggestions on a more elegant way to use isdigit/checking the input, I'd love to know. Thanks.

int checkInput ( char input [] ) 
{
	int iInput;
	while ( !isdigit(input[0]) ) 
	{	
		std::cout << "Please enter a valid number: ";
		std::cin >> input;
	}
	iInput = std::atoi ( input );
	return iInput;
}

void playSquare ( char grid [], char player, char input [] )
{
	int iInput = checkInput ( input );
	while ( iInput < 1 || iInput > 9 )
	{
		std::cout << "That number doesn't work. Try again: ";
		std::cin >> input;	
		iInput = checkInput ( input );
	}
	while ( grid[iInput-1] != '_' )
	{	
		std::cout << "That spot's been taken. Try again: ";
		std::cin >> input;
		iInput = checkInput ( input );
	}
    grid[iInput-1] = player;
}          

[Computergeek01]

I would make the while loop into a do while loop but I don't think that actually matters. Line 4 might be a problem since it only checks that one entry in the array.