C++ 二维数组索引错误

Question

I have a question regarding 2d array index. Here player_board is declared as a double pointer to char, which is a 2d array. Then I allocate the memory and everything seems to work just fine. x_vals and y_vals are two vectors that store x coordinates and y coordinates. I am trying to replace the original value of given x, y value with 'A'. When I print out the element of x_vals and y_vals it seems fine but when I use them as index, they begin to begin randomly assign. Here is my code...How should I solve this? Thx for helping

for(unsigned int i = 0; i < x_vals.size(); i++) {
    cout << x_vals.at(i) - 48 << y_vals.at(i) - 48 << endl;
    player_board[x_vals.at(i) - 48][y_vals.at(i) - 48] = 'A';
}

Answer 1

I'm assuming x_vals and y_vals are declared as vector of int or uint, thus when trying to obtain a cell at a certain index in a 2d dimentional matrix you might provide the matrix with negative values. For example lets say your x_val.at(1) = 10 -> then you will try to access the cell at index -38. Correct me if I'm wrong and kindly provide some more information about the types of x_vals and y_vals and the matrix allocation of player_board.

Answer 2

When you print out values of x_vals.at(i) - 48 and y_vals.at(i) - 48, are you not getting some negative values? I think you are getting these negative values and then trying to access a value in an array at a negative index eg player_board[-10]...

Maybe you could try using the absolute values of x_vals.at(i) - 48 and y_vals.at(i) - 48 as you index values

Also are you sure when you use the index values they do not go outside the declared range of your array.