Hi all! I'm new to Java, so please bear with me. I'm trying to calculate the average of grades input by the user. I keep getting a exception saying that it's dividing by 0. I can't figure out why.

import java.util.Random;
import java.util.ArrayList;
import java.util.Scanner;


public class Average
{
    // instance variables - this instance will get reader's name
    private Scanner reader;//name from user
    private Random random;//construct a Responder, declare a field type of Random
    ArrayList<Integer> grade = new ArrayList<Integer>();
    private String userName;//stores userName for later use.
    /**
     * Constructor for objects of class Calculator
     * Create a responder. 
     * Create the Random and ArrayList object.
     * Create the Scanner input object.
     */
    public Average()
    {
       reader = new Scanner(System.in); 
       random = new Random();
       grade = new ArrayList<Integer>();
       
    }
    /**
     * Saves userName for later use.
     */
    private String userName()
    {
       
        userName = reader.nextLine();
        return userName;
    }
    
    /**
     *Begin the program. This will print a welcome message
     *and start a dialog with the user.
     * 
     *
     * @return  A String typed by user.
     */
    public void start()
    {
             {
                
                 System.out.println("Welcome to the Test Grade Average Calculator");
                 System.out.println("What is your name?");
                 userName = reader.nextLine();
                 System.out.println("Hello, " + userName + ". You can find the average of your test grades.");
                 printWelcome();
            }
        }
        
    
    
    /**
     * Prints a welcome message to the screen
     */
    private void printWelcome()
    {
      
      
   
      System.out.println("Choose an action: (A) add a grade, (C) calculate average, (Q) quit.");
      
      String inputLine = reader.nextLine();
      if(inputLine.equalsIgnoreCase("A")){
          printA();
        }
      if(inputLine.equalsIgnoreCase("C")){
          printC();
        }
      if(inputLine.equalsIgnoreCase("Q")){
          printQ();
        }
       
    }
    /**
     * Print A initializes if user input is A for Addition.
     * @return A
     */
    
    private void printA()
    {
        
        Scanner reader = new Scanner(System.in);
        ArrayList<Integer> grade = new ArrayList<Integer>();
        {
            System.out.println("Enter a grade: ");
            int n = reader.nextInt();
            grade.add(n);

        }
        {
        printWelcome();
        }
    }
    
        /**
         * Print C calculates average stored from arraylist.
         * @return c
         */
This is where the issue is.
    private void printC()
    {
       
       int sum = 0;
       for(int i=0; i < grade.size(); i++){
           sum = sum + (grade.get(i));
        }
        int average = sum / grade.size();
        
        System.out.println("The average is " + average);
    }
    
    
    /**
     * Print M initializes if user input is M for Multiplication.
     * @return M
     */
    private void printQ()
    {
        System.out.println("Bye!");
    }
        
        
    }

The problem is in printA, you declare the grade array list, which hides the member variable of the same name. Remove this line:

ArrayList<Integer> grade = new ArrayList<Integer>();

Edited 6 Years Ago by kramerd: n/a

In your printA() method you have the line:

ArrayList<Integer> grade = new ArrayList<Integer>();

Which causes the grade ArrayList to be created again, erasing the older one. Remove this line and it should work fine :)

The problem is in printA, you declare the grade array list, which hides the member variable of the same name. Change this line:

ArrayList<Integer> grade = new ArrayList<Integer>();

to this

grade = new ArrayList<Integer>();

This will still cause the same problem since every time the user attempts to add a new number, the grade's constructor will be called again, erasing previous elements. Since the grade is being initialized in Average's constructor, this line can be removed.

Hi hwalsh,

private void printA()
    {
        
        Scanner reader = new Scanner(System.in);
        //ArrayList<Integer> grade = new ArrayList<Integer>();
        {
            System.out.println("Enter a grade: ");
            int n = reader.nextInt();
            grade.add(n);

        }
        {
        printWelcome();
        }
    }

The source of the problem is in the printA() method. The method is initializing a new local grade array list. Once the method completes the local grade object is destroyed (and hence the data along with it). Comment out the declaration and you should be fine.

Edit: kramerd and apines are too fast :D

You also want to check your printC() method. It's not calculating the average correctly. I recommend using the for loop to calculate the average and use a double for average so you can have a result of 92.5 for example.

HTH

Edited 6 Years Ago by Overbooked: n/a

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