Checking if a move has been made?

[VladTeppi]

Hello, I am currently making a Dots-And-Boxes program. I think it would be easiest to output the grid as a for loop. Example:

    for (int i=0; i<x; i++)
    {
        for (int a=0; a<x; a++)
        {cout<<"+ ";
        }
        cout<<endl;
    }

Well after a while, the user picks his points on the grid he wants to move. I don't know how to make it so I can check if that move has already been made. The user will select a move by inputting the x and y coordinates for the beginning and end points. I was wondering if someone could give me a good reference to go off of or some tips to for this project.