// represents one of our calculator buttons
// the order is how they will be added to the grid
public enum ButtonType {
    // row 1
    N1,
    N2,
    N3,
    PLUS,

    // row 2
    N4,
    N5,
    N6,
    MINUS,

    // row 3
    N7,
    N8,
    N9,
    TIMES,

    // row 4
    N0,
    DOT,
    SQRT,
    DIVIDE,

    // bottom pane
    EQUALS,
    CLEAR
}