The Internal Cursor Flag

    The mouse software maintains an internal flag that determines when the
    cursor should be displayed on the screen. The value of this flag is
    always 0 or less.

    . When the flag is 0, the cursor is displayed.

    . When the flag is 1, the cursor is hidden.

    Application programs cannot access this flag dirrectly. To change the
    flag's value, the program must call mouse functions 1, and 2. Function 1
    increments the flag; function 2 decrements it. Initially, the flag's
    value is -1, so a call to function 1 displays the cursor.

    Your program can call mouse function 0 or change screen modes to reset
    the flag to -1 and hide the cursor. Thus, it can always hide the cursor
    using just one call.

    Your program can call either function 1 or function 2 any number of
    times, but if it calls function 2, it must call function 1 later on to
    restore the flag's previous value. For example, if the cursor is on the
    screen and Your program calls function 2 five times, it must also call
    function 1 five times to get the cursor back on the screen.