📦 Compression & Decompression using C++

This project demonstrates a complete implementation of the LZW (Lempel–Ziv–Welch) compression algorithm with file I/O support.

• Compress text into integer codes
• Save/load compressed data from files
• Decompress codes back into the original text
• Verify correctness by comparing original and decompressed text

🧠 Theory – How LZW Works

LZW is a dictionary-based compression algorithm widely used in GIF and TIFF formats.
It works as follows:

1. Initialize Dictionary

   • Start with a dictionary of all single characters (ASCII 0–255).

2. Compression Process

   • Read characters and build the longest sequence already in the dictionary.
   • Output the dictionary code for that sequence.
   • Add the sequence + next character as a new entry to the dictionary.

3. Decompression Process

   • Use the codes to reconstruct text.
   • If a code isn’t in the dictionary yet, build it using the previous sequence + first character.
   • Add new entries while decoding.

⚙️ Build & Run

g++ main.cpp CompDec.cpp -o compdec
./compdec

🧪 Example Output

Reading input file 'input.txt'
Original Text: TOBEORNOTTOBEORTOBEORNOT

Compressing text...
Compressed Data: 84 79 66 69 79 82 78 79 84 256 258 260 
Compressed data saved to 'compressed.txt'

Decompressing...
Decompressed Text: TOBEORNOTTOBEORTOBEORNOT
Decompressed text saved to 'decompressed.txt'

Success: Decompressed text matches original!

🎯 Why This Project Matters

• Demonstrates the LZW compression algorithm, a widely studied and practical technique in data compression.
• Provides a clear C++ implementation including file I/O, dictionary-based encoding, and decoding.
• Shows a complete compression–decompression workflow: read → compress → save → load → decompress → verify.
• Serves as a foundation for extensions, such as binary storage, Unicode support, and performance optimizations.

🚀 Possible Improvements

• Binary storage: Save codes in binary instead of text for real size reduction.
• Unicode support: Extend dictionary beyond ASCII to handle UTF-8/UTF-16.
• Dictionary reset: Prevent unbounded growth by resetting or limiting size.
• Compression ratio: Display effectiveness (compressed_size / original_size).
• Streaming: Process large files in chunks instead of loading all at once.

📚 References

• Wikipedia – Lempel–Ziv–Welch (LZW)
• GeeksforGeeks – LZW (Lempel Ziv Welch) Compression technique