Printer-friendly version

% cat pi.cpp
// calculate pi from a series
# include <iostream>
# include <iomanip>
using namespace std;

int main()
{
  double sum, denom, sign;
  int n;

  // input data

  do
  {
     cout << "Enter the number of terms (must be greater than zero): " << endl;
     cin >> n;
  } while( n <= 0 );

  // initialize variables

  sum = 0.0;
  denom = 1.0;
  sign = 1.0;

  // calculate pi using a for loop

  for (int i=1; i <= n; i++ )
  {
      // cout << "sign = " << sign << " denom = " << denom
      // << endl; // diagnostic

      sum += sign * 4.0 / denom;

      denom += 2.0;
      sign = sign * (-1.0);

  }

  // output the result

  cout.setf(ios::fixed);
  cout.setf(ios::showpoint);
  cout.precision(4);

  cout << "The value of pi from the first "<< n
       << " terms of the series is " << sum << endl;

}
 

% g++ pi.cpp
% a.out
Enter the number of terms (must be greater than zero):
10
The value of pi from the first 10 terms of the series is 3.0418
% a.out
Enter the number of terms (must be greater than zero):
10000
The value of pi from the first 10000 terms of the series is 3.1415