Multiplying BigInts

Question

class   BigInt
{
private:
    string data;
    bool isNegative;
};

BigInt multiplication(BigInt left, BigInt right)
{
    BigInt sum;
    BigInt result;
    sum.da         


        

Answer 1

This is a solution from geeksforgeeks which is very similar to what you are trying to do. I modified it to fit your class there might be an error as I have not compiled it.

BigInt multiplication(BigInt num1, BigInt num2)
{
    int n1 = num1.data.size();
    int n2 = num2.data.size();
    if (n1 == 0 || n2 == 0)
       return "0";

    // will keep the result number in vector
    // in reverse order
    vector<int> result(n1 + n2, 0);

    // Below two indexes are used to find positions
    // in result. 
    int i_n1 = 0; 
    int i_n2 = 0; 

    // Go from right to left in num1
    for (int i=n1-1; i>=0; i--)
    {
        int carry = 0;
        int n1 = num1.data[i] - '0';

        // To shift position to left after every
        // multiplication of a digit in num2
        i_n2 = 0; 

        // Go from right to left in num2             
        for (int j=n2-1; j>=0; j--)
        {
            // Take current digit of second number
            int n2 = num2[j].data - '0';

            // Multiply with current digit of first number
            // and add result to previously stored result
            // at current position. 
            int sum = n1*n2 + result[i_n1 + i_n2] + carry;

            // Carry for next iteration
            carry = sum/10;

            // Store result
            result[i_n1 + i_n2] = sum % 10;

            i_n2++;
        }

        // store carry in next cell
        if (carry > 0)
            result[i_n1 + i_n2] += carry;

        // To shift position to left after every
        // multiplication of a digit in num1.
        i_n1++;
    }

    // ignore '0's from the right
    int i = result.size() - 1;
    while (i>=0 && result[i] == 0)
       i--;

    // If all were '0's - means either both or
    // one of num1 or num2 were '0'
    if (i == -1)
       return "0";

    // generate the result string
    string s = "";
    while (i >= 0)
        s += std::to_string(result[i--]);
    BigInt temp(s, num1.isNegative ^ num2.isNegative);
    return temp;
}

Hope this helps.