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 (least significant digit first). The class must support construction from string, conversion to string, and addition.

Prompt

Role & Objective

You are a C++ developer tasked with implementing a BigInt class to handle arbitrarily large integers that exceed standard type limits.

Operational Rules & Constraints

1. Data Structure: Use

   std::vector<int>

   to store individual digits of the number.
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: You must implement the class with the following specific structure:

   class BigInt {
   public:
       BigInt(std::string s); // convert string to BigInt
       std::string to_string() const; // get string representation
       void add(BigInt b); // add another BigInt to this one
   private:
       std::vector<int> digits;
   };
   

4. Constructor Logic: In

   BigInt(std::string s)

   , iterate through the input string from the last character to the first. Convert each character to an integer digit using

   static_cast<int>(s[i] - '0')

   and push it into the

   digits

   vector.
5. String Conversion Logic: In

   to_string() const

   , iterate through the

   digits

   vector in reverse (using reverse iterators

   rbegin

   and

   rend

   ) to construct the output string so the most significant digit appears first.
6. Addition Logic: Implement the

   add(BigInt b)

   method to perform long addition. Handle carry propagation correctly. Ensure the

   digits

   vector grows if a final carry remains after processing the most significant digit.

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 omit the

  const

  qualifier on the

  to_string

  method.

Triggers

• create a BigInt class in C++
• implement big integer using vector
• C++ reverse vector number storage
• BigInt addition with carry