Calculator Based on a Custom Lexer and State Machine Parser

A flexible parser and calculator engine developed using pure C++17 and the raw Win32 API. This project demonstrates compiler front-end mechanisms without relying on any external libraries (such as Qt, MFC, C#, etc.).

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🎯 Key Features & Design Decisions

1. Keyboard-Friendly & Parenthesis-Free Design (UX Decision)

To eliminate the time-consuming use of complex parentheses (e.g., Shift+8/9), this calculator is designed for parenthesis-free (linear input) entry. Users input expressions in a single line, and the system automatically manages operator logic in the background.

2. Custom p (Percentage) Operator

In addition to standard operators (+, -, *, /), a custom p (Percentage) operator has been added to facilitate financial calculations and speed up workflows.

• Formula: a p b → a * (b / 100)
• Example: The expression 1000 + 50 p 10 automatically calculates 50 p 10 = 5 first (due to operator precedence) and then produces the result 1000 + 5 = 1005.

3. Dynamic Win32 GUI Layout Engine

Instead of using hardcoded pixel values ​​for the interface, a VerticalLayout engine is implemented; it tracks element positions in memory and arranges them dynamically. This ensures that all elements automatically realign if the window size changes. ---

🧠 Technical Architecture

The project is structured into three main modules in accordance with software engineering principles: main.cpp (Interface & Event Loop), parser.h (Declarations), and parser.cpp (Implementation).

• Lexer (Scanner): Scans the source text character-by-character using std::wstring_view with zero-allocation semantics. It employs an LL(1) / One-Character Lookahead architecture based on peek() and advance() methods, requiring no backtracking.
• Parser (Interface / State Machine): Validates inputs using the ParserState enumeration (e.g., EXPECT_OPERAND, EXPECT_OPERATOR). It resolves token precedence using std::variant and a type-safe std::stack approach (Shunting-Yard-style State-Machine Parser).

🔮 Vision for x64 Opcode and Compiler Extensibility

In the current architecture, the eval() function operates like an interpreter, calculating results immediately. However, the front-end is designed to be fully modular. The infrastructure is ready to evolve into a compiler; by integrating a code generator into the eval() function in future stages, these simplified expressions can be directly converted into raw x64 Assembly or Opcode (Machine Code).

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🛠️ How to Compile?

1. Open any C++17-compatible compiler (Visual Studio MSVC is recommended). 2. Include main.cpp, parser.cpp, and parser.h in your project.
2. Compile by selecting the Windows (/SUBSYSTEM:WINDOWS) subsystem setting.