unable to get the following part in CRC implementation in c-CodePudding

So i was referring Geeks For Geeks for the implementation of CRC in Data Communication
Here is the code:-

#include <bits/stdc  .h>
using namespace std;

string xor1(string a, string b)
{
  string result = "";
  int n = b.length();
  for (int i = 1; i < n; i  )
  {
    if (a[i] == b[i])
      result  = "0";
    else
      result  = "1";
  }
  return result;
}

string mod2div(string divident, string divisor)
{
  int pick = divisor.length();
  string tmp = divident.substr(0, pick);
  int n = divident.length();
  while (pick < n)
  {
    if (tmp[0] == '1')
      tmp = xor1(divisor, tmp)   divident[pick];
    else
      tmp = xor1(std::string(pick, '0'), tmp)   divident[pick];
    pick  = 1;
  }
  if (tmp[0] == '1')
    tmp = xor1(divisor, tmp);
  else
    tmp = xor1(std::string(pick, '0'), tmp);
  return tmp;
}

void encodeData(string data, string key)
{
  int l_key = key.length();
  string zeroes_to_be_added;
  for(int i=0;i<l_key-1;i  )
    zeroes_to_be_added = zeroes_to_be_added   "0";
  string appended_data = (data   zeroes_to_be_added);
  string remainder = mod2div(appended_data, key);
  string codeword = data   remainder;
  cout << "Remainder : " << remainder << "\n";
  cout << "Encoded Data (Data   Remainder) :" << codeword << "\n";
}

int main()
{
  string data,key;
  cout<<"enter the data to be send to the receiver side from the sender side"<<endl;
  cin>>data;
  cout<<"Enter the key value that is present on both sender and reciever side"<<endl;
  cin>>key;
  encodeData(data, key);
  return 0;
}

i get all the code except the below one :-

string mod2div(string divident, string divisor)
{
  int pick = divisor.length();
  string tmp = divident.substr(0, pick);
  int n = divident.length();
  while (pick < n)
  {
    if (tmp[0] == '1')
      tmp = xor1(divisor, tmp)   divident[pick];
    else
      tmp = xor1(std::string(pick, '0'), tmp)   divident[pick];
    pick  = 1;
  }
  if (tmp[0] == '1')
    tmp = xor1(divisor, tmp);
  else
    tmp = xor1(std::string(pick, '0'), tmp);
  return tmp;
}

could someone can help me in getting to understand this part lets say for the data = 1010101010 and the key = 11001.

issue:- What is the use of this like what exactly this part is doing:-

std::string(pick, '0')

Any help will be appreciated.

CodePudding user response：

std::string(pick, '0') is the string constructor creating a string of length pick filled with '0'. In other ways it's the short form of the following code :-

  string zeroes_to_be_added;
  zeroes_to_be_added.resize(pick);
  for (int i = 0; i < pick; i  )
    zeroes_to_be_added[pick] = '0';