Spreadsheet Application

A fully-featured spreadsheet built in C# with WinForms, implementing expression trees, the command pattern, XML persistence, and reactive cell dependencies.

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Table of Contents

1. Overview
2. Features
   • Cell Editing
   • Formula Evaluation
   • Supported Operators
   • Cell Background Color
   • Undo / Redo
   • Save / Load
   • Clear
3. Error Handling
4. Unit Testing
5. Getting Started

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Overview

This project was developed for CPT_S 321 at Washington State University under Professor Vanera Arnaoudova. It is a Windows Forms spreadsheet application written in C# (.NET 10) that demonstrates a range of software engineering concepts:

• Expression trees with Shunting-yard algorithm (infix → postfix)
• Operator extensibility via reflection
• Reactive cell dependency graph with circular reference detection
• Undo/redo via the Command design pattern
• XML-based save/load with robust error recovery
• Unit-tested engine (NUnit) decoupled from the UI layer

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Features

Cell Editing

Click any cell to select it; double-click (or begin typing) to enter edit mode. Each cell maintains two distinct values:

• Text — the raw input as entered by the user (e.g. =A1+B1 or hello)
• Value — the evaluated display value (e.g. 42)

While editing, the cell displays its raw Text. On commit, it switches back to showing the computed Value.

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Formula Evaluation

Prefix a cell's content with = to enter formula mode:

=A1 + B2 * 3
=(C3 - 1) / D4

Formulas are evaluated using a binary expression tree:

1. The infix expression (after stripping =) is tokenized and converted to postfix notation using the Shunting-yard algorithm.
2. A tree of ConstantNode, VariableNode, and OperatorNode objects is constructed from the postfix token stream.
3. The tree is evaluated recursively.

Cell references (e.g. B3) are treated as variables. When a referenced cell's value changes, all dependent cells automatically re-evaluate via a PropertyChanged subscription graph.

Cell names are case-sensitive. Whitespace inside formulas is ignored.

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Supported Operators

Symbol	Operation	Precedence
+	Addition	1
-	Subtraction	1
*	Multiplication	2
/	Division	2

Operators are registered at runtime using C# reflection — the factory scans the assembly for all OperatorNode subclasses and maps their Operation character automatically. Adding a new operator (e.g. ^ for exponentiation) requires only a new class; no factory changes needed.

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Cell Background Color

Select one or more cells, then navigate to Cell → Change Background Color to open a color picker. The chosen color is applied to all selected cells simultaneously. Color changes are fully undoable.

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Undo / Redo

Action	Shortcut	Menu
Undo	—	Edit → Undo
Redo	—	Edit → Redo

Undo/redo is implemented with the Command design pattern. Every mutating action (text edit, color change) is wrapped in an ICommand object and pushed onto an undo stack. Each command knows how to produce its own reverse via GetReverse().

• Undo — pops from the undo stack, executes the reverse, pushes to redo stack.
• Redo — pops from the redo stack, executes the reverse, pushes back to undo stack.

The menu items dynamically display the action name (e.g. Undo text change, Redo color change) and are disabled when the respective stack is empty. The Clear operation resets both stacks and cannot be undone.

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Save / Load

Navigate to File → Save or File → Load to persist and restore spreadsheet state as an XML file.

Only cells that differ from their defaults (non-empty text or non-white background) are written, keeping files compact:

<spreadsheet>
  <cell>
    <name>B3</name>
    <text>=A1+1</text>
    <color>FFFF0000</color>
  </cell>
</spreadsheet>

On load, the spreadsheet is first cleared, then each cell is restored in document order. Malformed or unrecognized XML is handled gracefully with user-facing error dialogs rather than crashes.

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Clear

File → Clear resets every cell to its default text and color, and empties both undo and redo stacks.

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Error Handling

When a formula cannot be evaluated, the cell's display value is set to a descriptive error string rather than throwing an unhandled exception.

Display Value	Cause
invalid variable	A token in the formula is not a valid cell name (e.g. =hello, =g6 due to case sensitivity)
self reference	The formula directly or indirectly references its own cell
circular reference	A cycle exists in the cell dependency graph (e.g. A1 → B2 → C3 → A1)
unsupported operator	The formula contains an operator that is not registered in the factory
unknown error	Any other unexpected exception during evaluation

When a circular reference is resolved (e.g. by editing one of the cells in the chain), all affected cells re-evaluate automatically.

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Unit Testing

Tests are located in Spreadsheet_Testing/ (NUnit, targeting net10.0-windows) and ExpressionTreeTesting/ (NUnit, targeting net10.0).

SpreadsheetEngine tests cover:

• Default BGColor is 0xFFFFFFFF
• PropertyChanged fires on color mutation but not on no-op assignment

ExpressionTree tests cover:

• Constants, single variables, and multi-variable expressions
• All four arithmetic operators with correct precedence
• Parenthesis grouping and nesting
• Left-to-right associativity for same-precedence chains
• Variable re-assignment (latest value wins)
• Empty expression evaluates to 0.0
• Mismatched parentheses evaluate to 0.0

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Getting Started

Requirements: .NET 10 SDK, Windows (WinForms)

# Clone the repository
git clone <repo-url>
cd Spreadsheet_Thomas_Nguyen

# Build and run
dotnet run --project Spreadsheet_Thomas_Nguyen/Spreadsheet_Thomas_Nguyen.csproj

# Run tests
dotnet test

Or open Spreadsheet_Thomas_Nguyen.slnx in Visual Studio 2022+ and press F5.

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Copyright © 2026 Thomas Nguyen · MIT License