Multiply large numbers as strings

This algorithm is very much like factorial. Multiplication of very large numbers represented as strings because they go out of the integer range.

#include <iostream>
#include <vector>
#include <string>
#include <sstream>

std::string multiply(std::string a, std::string b) {
  // take a vector of length 200 and initialize all of its elements to 0.
  std::vector<int> multiplication(200, 0); 

 int place = 0;
 for(int i = a.size() - 1 ; i >= 0; i--){
   int carry = 0;
   std::vector<int>::iterator it = multiplication.begin() + place;
   for(int j = b.size() - 1 ; j >= 0; j--){
     int a_element = a[i] - '0';
     int b_element = b[j] - '0';
     int prod = a_element*b_element + carry + *it;
     *it = prod % 10;
     carry = prod / 10;
     it++;
     while (carry){
       int current_carry = carry + *it;
       *it += current_carry % 10;
       it++;
       carry = current_carry / 10;
    }
  }
   place++;
 }

std::stringstream ss;
for(int i = multiplication.size(); i >= 0; i--){
 ss << multiplication[i];
}
 return ss.str();
}

Author: Saurabh Purnaye

Sr. Developer @NYSE @ICE_Markets. Low Latency Trading, Linux, C++, Python, Ruby. pursuing certificate in #QuantFinance and Passed CFA L1

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