Is variable shared in ASP.NET C#?

When I define a variable as below:

public static int x;

The program works properly but the variable is shared by users who enter the site. So the program doesn't work when users access at same time.

If I define a variable as below:

private int x;

the program doesn't work properly. for example, Can't find where checkbox true is.

The below code is for finding where the user check changed most recently.

public static CheckBox[,] cbs = new CheckBox[14, 28];
public static bool[,] diffmap = new bool[14, 28];

or

private CheckBox[,] cbs = new CheckBox[14, 28];
private bool[,] diffmap = new bool[14, 28];



protected void CBs_CheckedChanged(object sender, EventArgs e)
{
    int cur_x = 0;
    int cur_y = 0;

    int num_reserve = 0;

    for (int i = 0; i < 14; i++)
    {
        for (int j = 0; j < 28; j++)
        {
            if (cbs[i, j].Checked != diffmap[i, j])
            {
                cur_x = i;
                cur_y = j;
                break;
            }
        }
    }


    for (int i = 0; i < 14; i++)
    {
        for (int j = 0; j < 28; j++)
        {
            diffmap[i, j] = cbs[i, j].Checked;
        }
    }

}