Chris Pollett>Old Classes>PIC 10a, Spring 2000>Hw6>Hw6 FAQ

General questions and answers for this homework will be placed here as they arise.

1. In the constructor it would be useful to be able to convert an integer to a SquareValues, how do I do this? This problem comes up when you try to calculate the number of bombs in adjacent squares for a board piece. If you add one to something of type SquareValues, C++ coerces the result to something of type int. To make it a SquareValues again you do: (SquareValues)(...your expression). For example,
   SquareValues a = (SquareValues)(ONE_UNSEEN +1); would set a to be TWO_UNSEEN.
2. How do I dynamically allocate a 2-dimensional array? You need to do this for the board in the minesweeper game. Here is an example for dynamically allocating an 2D-array of integers of size rowsXcolumns. First, such a 2D-array is referenced by a pointer to a pointer. We can declare this as

   int **arr, rows, columns;
   cin >> rows; //get values for the size of the array from user
   cin >> columns;
   

   We then allocate the rows...

   arr = new int* [rows];
   

   So arr is used to store the address of the location of where the first row will be store. *arr (also written arr[0]) will be the location of the 0th row. arr[1] will be the address of the first row, etc. We now have to allocate memory for these rows...

   for(int i=0; i < rows; i++)
   {
   	arr[i] = new int[columns];
   }
   

   At this point our 2D-array is created and we can use it as regular 2D-array.
3. How do I deallocate a dynamically allocated 2D-array? The idea is just the reverse process of the allocation above.

   for(int i=0; i < rows; i++)
   {
   	delete [] arr[i]; //delete's memory for row i
   }
   delete [] arr; //deletes the pointers to the rows.
   

4. What is the member function ~MineSweeper()? This is the destructor for the class MineSweeper. When a object of a class is deleted this destructor method is automatically called. The point of a destructor is to free up any dynamically allocated memory that the object might have used.