/* 
   An object of class StatCalc can be used to compute several simple statistics
   for a set of numbers.  Numbers are entered into the dataset using
   the enter(double) method.  Methods are provided to return the following
   statistics for the set of numbers that have been entered: The number
   of items, the sum of the items, the average, and the standard deviation.
*/

public class StatCalc {

   private int count;   // Number of numbers that have been entered.
   private double sum;  // The sum of all the items that have been entered.
   private double squareSum;  // The sum of the squares of all the items.

   public void enter(double num) {
         // Add the number to the dataset.
      count++;
      sum += num;
      squareSum += num*num;
   }

   public int getCount() {   
         // Return number of items that have been entered.
      return count;
   }

   public double getSum() {
         // Return the sum of all the items that have been entered.
      return sum;
   }

   public double getMean() {
         // Return average of all the items that have been entered.
         // Value is Double.NaN if count == 0.
      return sum / count;  
   }

   public double getStandardDeviation() {  
        // Return standard deviation of all the items that have been entered.
        // Value will be Double.NaN if count == 0.
      double mean = getMean();
      return Math.sqrt( squareSum/count - mean*mean );
   }

}  // end of class StatCalc