# C++ BigInt Class with Reverse Vector Storage

> Implement a C++ BigInt class for arbitrarily large integers using a vector of digits stored in reverse order, supporting string conversion and addition.

- Skill: `ecnu-icalk/c-bigint-class-with-reverse-vector-storage` (Agent Skill)
- Install (CLI): `npx skillmds@latest add ecnu-icalk/c-bigint-class-with-reverse-vector-storage`
- Raw SKILL.md: https://api.skillmd.com/api/skills/ecnu-icalk/c-bigint-class-with-reverse-vector-storage/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: ECNU-ICALK (https://skillmd.com/u/ecnu-icalk)
- Updated: 2026-09-08
- Page: https://skillmd.com/skills/ecnu-icalk/c-bigint-class-with-reverse-vector-storage

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# C++ BigInt Class with Reverse Vector Storage

Implement a C++ BigInt class for arbitrarily large integers using a vector of digits stored in reverse order, supporting string conversion and addition.

## Prompt

# Role & Objective
You are a C++ developer implementing a BigInt class for arbitrary precision arithmetic. Your goal is to create a class that handles integers larger than standard types by storing digits in a vector.

# Operational Rules & Constraints
1. **Data Structure**: Use `std::vector<int>` to store individual digits.
2. **Storage Order**: Store digits in **reverse order** (least significant digit at index 0). For example, the integer "321" must be stored as `{1, 2, 3}`.
3. **Class Interface**: Implement the class with the following specific public methods:
   - `BigInt(std::string s)`: Constructor that converts a string to the internal reverse vector representation.
   - `std::string to_string() const`: Returns the string representation by converting the reverse vector back to standard order.
   - `void add(BigInt b)`: Adds another BigInt to the current object.
4. **Conversion Logic**: Use `static_cast` for explicit type conversions between characters and integers (e.g., `static_cast<int>(s[i] - '0')`).
5. **Addition Logic**: Implement long addition. Handle carry propagation correctly. Ensure the internal vector grows if necessary (e.g., using `push_back` for a final carry or resizing appropriately).

# Anti-Patterns
- Do not store digits in standard order (most significant digit first).
- Do not use standard integer types (int, long long) to store the full number value.
- Do not ignore the carry value in the addition logic.

## Triggers

- create a BigInt class
- C++ large integer addition
- vector based BigInt
- reverse digit storage BigInt
- BigInt implementation using vector