Question

Write a program that calculates the average of a stream of non-negative numbers. The user can enter as many non-negative numbers as they want, and they will indicate that they are finished by entering a negative number. For this program, zero counts as a number that goes into the average. Of course, the negative number should not be part of the average (and, for this program, the average of 0 numbers is 0).

You must use a method to read in the numbers, keep track of the running sum and count, compute the average, and return the average to the main() method. Note that you must use a loop to do this, as you don't know how many numbers the user will enter ahead of time.

The main() method must print the average (which was returned from your method) using two decimal places, and then ask the user if they want to repeat the entire process. The user should be allowed to repeat the process as many times as they wish. This means you will have a loop in your main() method that instructs the user what to do, calls your average method, reports the result, and finally asks the user if they want to calculate another average for a different set of numbers. Importantly, your program will not function correctly if is more than one Scanner object looking to the keyboard. Thus, since both main() and your averaging method need to get input from the keyboard, you will have to declare and initialize a Scanner variable in main(), then pass it as an argument to the averaging method. Furthermore, note that your method that reads in the numbers and computes the average must have no System.out.println() statements -all output must happen in main(). Be sure you take the time to think through the pieces and, more importantly, implement in small steps. I suggest you proceed like so:

1. Get the structure of defining and calling your method down first, with no loops involved.

2. Fill in the method with a loop that runs while the user enters non-negative numbers.

3. Modify the loop to keep track of the sum and count, then print the average in the function.

4. Modify the method to actually return the average.

5. Modify main() to use another loop to ask the user if they want to repeat the entire calculations

Answer 1

Java Program:

/* Java Program that reads in non negative integers from user and prints their sum and average */

import java.util.Scanner;

//Class definition
class IntegerAverage
{
   //Method that returns the average of values entered by user
   public static double getAverage(Scanner ip)
   {
       int temp, sum = 0, cnt = 0;
      
       double avg;
      
       //Reading a number
       System.out.print("\n Enter a Non-Negative Number: ");
       temp = ip.nextInt();
      
       //Loop till user enters a negative number
       while(temp >= 0)
       {
           //Calculating sum
           sum += temp;
          
           //Updating number of elements
           cnt++;
          
           //Reading a number
           System.out.print("\n Enter a Non-Negative Number: ");
           temp = ip.nextInt();
       }
      
       //Calculating average
       avg = sum / (double) cnt;
      
       //Return average
       return avg;
   }
  
   //Main method
   public static void main(String args[])
   {
       String userChoice;
      
       //Scanner object
       Scanner sc = new Scanner(System.in);
      
       //Loop till user want to stop
       do
       {
           //Calling method and printing average
           System.out.println("\n Average: " + getAverage(sc));
          
           sc.nextLine();
          
           //Reading user choice
           System.out.print("\n Do you want to continue? (Press Y/y): ");
           userChoice = sc.nextLine();
          
       //While condition check  
       }while(userChoice.charAt(0) == 'Y' || userChoice.charAt(0) == 'y');
   }
}

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Sample Output:

C:Windowslsystem32\cmd.exe Dav>javac IntegerAverage. java D:Java> java IntegerAverage Enter a Non-Negative Number: 10 Enter a Non-Negative Number: 20 Enter a Non-Negative Number: 30 Enter a Non-Negative Number: 40 Enter a Non-Negative Number: -55 Average: 25.0 Do you want to continue? (Press Y/y): y Enter a Non-Negative Number: 65 Enter a Non-Negative Number: 45 Enter a Non-Negative Number: 22 Enter a Non-Negative Number: 89 Enter a Non-Negative Number: 45 Enter a Non-Negative Number: -2 Average: 53.2 Do you want to continue? (Press Y/y): n DJava>