配列に格納された大きな数値を加算するときに適切な桁上げ伝播を保証するにはどうすればよいですか?

struct Adder {
  // Array to store the digits
  unsigned short digits[n];
  // Flag to handle carry
  unsigned short carry;

  // Constructor to initialize the adder
  Adder() {
    for (int i = 0; i < n; i++) {
      digits[i] = 0;
    }
    carry = 0;
  }

  // Function to add two digits with carry propagation
  void addWithCarry(unsigned short a, unsigned short b) {
    unsigned short sum = a + b + carry;
    digits[i] = sum % 10; // Store the last digit (0-9)
    carry = sum / 10;      // Carry for the next digit
  }

  // Function to perform addition on the entire array
  void add(const Adder& rhs) {
    for (int i = 0; i < n; i++) {
      addWithCarry(digits[i], rhs.digits[i]);
    }
  }
};