Dynamic Array

#include <fstream>

#include <iostream>

using namespace std;

int main()

{

  double a,b;

  int n;

  n=0;

  ifstream f ("data.txt", ios::in);

  

  // Opening and reading the file for the first time 

  // to count the number of (x, y) data pairs. 

  if (f.is_open())

  {

    while (!f.eof())

    {

      f>>a>>b;

      if (f.eof())break;

      n++;

      cout << a <<" "<<b<<" "<<n<<"\n";

    } 

    cout <<"n="<<n<<"\n";

    f.close();

  }

   else cout << "Unable to open file"; 

   f.close();

    

  // Declaration of dynamic arrays x and y.

  double * x,* y;

  x=new double [n];

  y=new double [n];

  // Opening and reading the file for the second time 

  // to input of (x, y) data pairs to dynamic arays x and y.     

  int i=0;

  f.open ("data.txt", ios::in);

    if (f.is_open())

  {

    while (!f.eof())

    {

      f>>a>>b;

      if(f.eof())break;

      x[i]=a;

      y[i]=b;

      cout << x[i] <<" "<<y[i]<<" "<<i<<"\n";

      i++;

    } 

  f.close();

  }

   else cout << "Unable to open file secomd time\n"; 

      return 0;

}