💳 Credit Card Validator (C++)

A tiny, fast C++ console app that validates credit card numbers using the Luhn algorithm.
Type a card number, get VALID / INVALID with basic stats. No dependencies.

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✨ Features

• ✅ Luhn algorithm validation
• 🔢 Digits-only and length checks (13–19)
• 🧹 Simple, robust I/O handling
• 💻 Works on macOS/Linux/Windows (console)

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🛠 Requirements

• C++17 or later
• A C++ compiler (e.g., g++, clang++, or MSVC)
• Terminal/Console

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🚀 Build & Run

🐧 macOS / Linux

g++ -std=c++17 -O2 -Wall -Wextra -o credit-card-validator src/main.cpp
./credit-card-validator

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🪟 Windows (MinGW)

g++ -std=c++17 -O2 -Wall -Wextra -o credit-card-validator.exe src/main.cpp
credit-card-validator.exe

⚙️ Using CMake (All Platforms) (optional)

mkdir build && cd build
cmake ..
cmake --build .
# Run
./credit-card-validator   # macOS / Linux
credit-card-validator.exe # Windows

🧪 Example

Enter credit card number (no spaces): 4539578763621486

Card Number: 4539578763621486 Length: 16 digits Status: ✅ VALID

🧠 How It Works (Luhn in 10 seconds)

1.	Traverse the number from right to left.
2.	Double every second digit; if result > 9, subtract 9.
3.	Sum all digits.
4.	If sum % 10 == 0 → VALID, else INVALID.