013.cpp

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#include <iostream>
#include <fstream>
using namespace std;

typedef unsigned long long verylong;
const verylong digits = 1e18;
const int length = 18;
const int gps = 4;
class bigN
{
//spilt into 16 groups, each with 19 digits
//smallest place unit exists in x[0]
  verylong x[gps];
public:
    bigN ()
  {
    for (int k = 0; k < gps; k++)
      x[k] = 0;
  }
  bigN (char str[51])
  {
    for (int k = 0, idx = 49; idx >= 0; k++, idx -= length)
      {
        x[k] = 0;
        for (int i = idx - length + 1; i <= idx; i++)
          if (i >= 0)           //the last segment may be shorter than 18 digits.
            x[k] = x[k] * 10 + (str[i] - '0');
      }
  }

  void operator+= (bigN * Y)
  {
    for (int k = 0; k < gps; k++)
      x[k] += Y->seg (k);
    for (int k = 0; k < gps - 1; k++)
      if (x[k] > digits)
        {
          x[k + 1] += x[k] / digits;
          x[k] %= digits;
        }
  }
  verylong seg (int k)
  {
    return x[k];
  }
  verylong last_segment ()
  {
    int k = gps - 1;
    while (x[k] == 0)
      k--;

    return x[k];
  }
  /*
     void printN()
     {
     cout << '(' << x[0];
     for(int k=1;k<gps;k++)
     cout  << ','<< x[k];
     cout << ')' << endl;
     } */
};

void
import (bigN ** N)
{
  ifstream input;
  input.open ("013.txt");

  char str[51];
  for (int k = 0; k < 100; k++)
    {
      input >> str;
      N[k] = new bigN (str);
    }
}

int
main ()
{
  bigN *N[100];
  import (&(N[0]));

  bigN Sum;
  for (int k = 0; k < 100; k++)
    Sum += N[k];

//Sum.printN();
  cout << "The sum is " << Sum.last_segment () << "..." << endl;
  return 0;
}