Files

• recursive_simple.cpp — Recursive version using unsigned long long. Short and didactic; overflows for n > 20.
• bigint_iterative.cpp — Iterative big-integer version using a vector of base-10 digits. Computes exact factorials for much larger n without external libraries.
• factorial_comparison.md — Comparison notes and guidance for publication.

How to build

GCC / Clang

g++ -std=c++17 -O2 recursive_simple.cpp -o recursive_simple
./recursive_simple

g++ -std=c++17 -O2 bigint_iterative.cpp -o bigint_iterative
./bigint_iterative

MSVC (Developer Command Prompt)

cl /EHsc recursive_simple.cpp
recursive_simple.exe

cl /EHsc bigint_iterative.cpp
bigint_iterative.exe

Quick comparison

• Recursive (native): minimal code; limited by 64-bit overflow and recursion depth.
• Big-int (digit vector): exact results for large n; simple implementation but not optimized for thousands of digits — prefer boost::multiprecision::cpp_int or GMP for production.

Suggested tutorial flow

1. Introduce factorial mathematically.
2. Show recursive native implementation and explain overflow and stack-depth limits.
3. Show iterative native implementation and discuss limits.
4. Present big-integer approach (this repo) and explain complexity.
5. Demonstrate using boost::multiprecision::cpp_int and compare performance.
6. Optional: link to advanced algorithms (prime-swing, binary splitting) for very large factorials.