Step

Create the classes Spreadsheet, SpreadsheetSumSheet, CellAverageSheet, and SpreadSheetViewContainer

Project: P2 - Spreadsheets (Janak)

Parent: Build the Program: Cell classes and spreadsheet classes

Create the classes:

Spreadsheet, which knows its value and sheetType and deals with the interface to the outside world.
SpreadsheetSumSheet, which keeps track of its sheets that it's going to sum.
CellAverageSheet, which keeps track of the cells that it's going to average.
SpreadSheetViewContainer, which is the view for the Spreadsheet

Generic form of this step: How to build a GUI using the C+N library