Thread: what did I do wrong?

Boy, I sure would love it if someone could help me figure this out. My professor has created some code that's a loop for enter numbers. I need to add code to make the program figure averages and standard deviation. I've added the formulas as I believe they should be, and the program runs, but when I test the program with some small numbers I can do in my head, the average and deviation is wrong. Here's the code, stripped of pretty formatting....

Code:

// Program Abstract:       the purpose of this program is to determine the average and standard deviation of input numbers
//   Input Required:       list of numbers
//   Output Desired:       program will output the list of numbers,
//                         average and standard deviation of each number
// =============================================================================

#include <conio.h>
#include <fstream.h>
#include <iomanip.h>
#include <iostream.h>
#include <math.h>

//==============================================================================

// variable declarations

// alphabetized variable dictionary
// =========================================================================
// d is data
// i is spacing
// m is average
// n is count
// reply stores user's answer to queries
// s is standard deviation
// x is sum

int main() {
  double d, i, m, n, s, x;
  double average, stddev, sum, sumsqr;
  char reply;

ofstream fout;

  fout.open ("prompt.txt");

  // introduce the program to determine average and
  // standard deviation of a list of numbers

//==============================================================================
  cout << setw (61) << "Program for average and standard deviation";

  // press any key to continue
  cout << setw (52) << "Press RETURN to continue";
  getchar();

  // run program until user is done
  // loop for data entry, calculates sum and counter, ends after last while
  do
    {
      // setting beginning numbers to 0
      n = 0;
      x = 0;
      sumsqr = 0;

      // loop B check and correct data entry
      do
        {
          clrscr ();

          // prompt the user for the next data
          cout << setw (61) << "Enter next data, enter -1 to end data stream";
          cout << ": ";
          cin >> d;

          do
            {
              clrscr ();

                // echo print data read
                cout << setw (37) << "Is " << d << " correct?";
                cout << endl << endl << endl;

                // query the user for correctness of input data
                cout << setw (55) << "Enter y for yes or n for no: ";

                // input response to query
                cin >> reply;
                tolower(reply);
      }

      while(reply!='n' && reply!='y');


      if(reply=='y') {

            ++n ;
            x += d;
            sumsqr += d * d;

            // record verified data in output textfile
            fout << d << endl;
          }
    }
        while (d != -1);

        // calculate average
        if ( n > 0 )
          m = x / n;
        else
          m = 0 ;

        // press any key to continue
        cout << setw (52) << "Press RETURN to continue";
        getchar();

        // calculate standard deviation
        if ( n > 1 )
          s = sqrt ((n * sumsqr - x * x) / (n * (n - 1))) ;
        else
          s = 0;

        clrscr ();

        cout << setw (50) <<  "The average is: " << m;

        cout << setw (50) <<  "The standard deviation is: " << s;

        // press any key to continue
        cout << setw (52) << "Press RETURN to continue";
        getchar();

        do
          {
            clrscr ();

            // query user for another input data
            cout << setw (55) << "Is there another set of data?";

            cout << setw (55) << "Enter y for yes or n for no: ";
            cin >> reply;
            tolower(reply);
          }
        while ((reply != 'n') && (reply != 'N') &&
               (reply != 'y') && (reply != 'Y'));
      }
    while ((reply == 'y') || (reply == 'Y'));

    fout.close ();
    return 0;
  }