Math Expression Evaluator (Client-Server using epoll)

A client-server system built in C for evaluating mathematical infix expressions using the two-stack algorithm. It uses epoll for concurrent client handling and supports negative numbers, unary minus, and parentheses.

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📁 File Structure

math-eval-epoll/
├── client.c          // Connects to the server and sends expressions
├── server.c          // Handles multiple clients using epoll, processes expressions
├── eval.c            // Validates and evaluates infix expressions
├── eval.h            // Declarations for eval.c functions
├── stack.c           // Generic stack implementation using arrays
├── stack.h           // Header for stack operations
└── README.md         // Project documentation

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🚀 Usage

1. Compile the project

gcc stack.c eval.c server.c -o server

gcc client.c -o client

2. Run the server

./server

3. Run the client (in a separate terminal)

./client

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🔧 Workflow

Client Side

1. Connects to server using TCP.
2. Displays welcome message and rules.
3. Sends expressions and receives evaluated results.
4. Supports quitting with inputs like exit, n, or No.

Server Side

1. Accepts new connections using epoll (non-blocking I/O).
2. Sends rules and prompt to each new client.
3. For each expression received:
   • Checks for ambiguous spacing (e.g., 34 5).
   • Validates the input as a correct infix expression.
   • Evaluates using the two-stack algorithm.
   • Sends the result or an appropriate error.
4. Gracefully closes connection if the client chooses to quit.

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🔍 Evaluation Logic

• Uses a two-stack approach:
  • One stack for operands (integers).
  • One stack for operators (+, -, *, /, %, (, )).
• Supports unary minus, including:
  • Negative numbers like -5
  • Nested negations like -(-(5))
• Handles operator precedence and parenthesis evaluation.

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📚 Concepts Demonstrated

• C Socket Programming (TCP)
• epoll for efficient I/O multiplexing
• Dynamic, generic stack implementation
• Mathematical expression parsing and evaluation
• Unary operator handling in infix expressions

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📜 Example Expressions

Expression	Result
23 + 4 - 12 * (4 * 6)	-261
34 + 56 - 7 + -(11 * -2)	98
32 + (-(-5) + -12 * 6)	-35
-5 * (2 + 3)	-25

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🛡️ Input Validation

• ❌ 23 45 → Rejected due to ambiguous spacing
• ❌ 5 + * 4 → Rejected due to invalid infix
• ✅ -5 + (3 * 2) → Valid expression

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💻 Screenshots

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📌 Notes

• Works on Linux natively.
• Windows users can run it via WSL (Windows Subsystem for Linux).

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🔗 References

• Beej's Guide to Network Programming
• Linux epoll man page
• The Linux Programming Interface by Michael Kerrisk

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📄 License

This project is licensed under the MIT License.