import java.util.Scanner;

/* Java application that reports the arithmetic mean (i.e., average) 
** of the integer values supplied to it by the user.  The program
** prompts the user to enter each value; -9999 signals end-of-input.
*
*  Author: R. McCloskey (based on a program by Paul Jackowitz)
*  Date: August 24, 2010; updated August 2020; updated Sept. 2021
*/

public class MeanProgram {

   // "Sentinel" value that, when entered by the user, signals that 
   // there is no more input to be processed.
   private static final int EOF_SENTINEL = -9999;

   // A Scanner object can read data from an input source;
   // here that will be the user's keyboard.
   private static Scanner keyboard = new Scanner(System.in);

   // When a Java application is run, execution begins in the main() method. 
   public static void main(String[] args) {    
      int inputVal;   // the most recent input entered by the user
      int sumSoFar;   // the sum of inputs entered so far
      int count;      // the # of inputs entered so far
      double mean;    // the result
      
      sumSoFar = 0;  count = 0;   // obvious initializations

      // read first input value
      inputVal = getAnInput();

      // accept and process input values until a zero value is entered
      while (inputVal != EOF_SENTINEL) {
         sumSoFar = sumSoFar + inputVal;  // add latest input to running total
         count = count + 1;               // increment counter
         inputVal = getAnInput();         // read next input via method call
      }

      // now report the result
      System.out.print("The mean of the integers entered is "); 
      if (count > 0) {
         mean = (double)sumSoFar / (double)count;
         System.out.println(mean);
      }
      else {
         System.out.println("undefined");
      }
   }

   /* Prompts the user to enter an input, accepts the response,
   ** and returns it to the caller.
   */
   private static int getAnInput() {
      System.out.printf("Enter an integer (%d to quit): ", EOF_SENTINEL);
      return keyboard.nextInt();
   }

}