Logic Error with Summing Up Columns [Java]

Question

This is very similar to this post except that the code is now part of an object instead of a method.

Again, this is how it should look:

Enter 3 rows and 4 columns:

1 2 3 4
5 6 7 8
9 10 11.2 12.5

You entered:

1.0 2.0 3.0 4.0
5.0 6.0 7.0 8.0
9.0 10.0 11.2 12.5

The sums are:

15.0 18.0 21.2 24.5

This is my code:

else if (choice == 2) {

    // Prompt user
    System.out.println("You Selected Sum Columns");

    // Enter array values
    double[][] myList = new double[3][4];
    double[][] userList = new double[3][4];

    feature2 f2 = new feature2();

    f2.run(myList, input);

    f2.getInput(userList);

}

and

import java.util.Scanner;

public class feature2 {

    public void run(double[][] myList,Scanner input) {


        // 2D arrays are like spreadsheets ROW and Columns
        System.out.println("Enter " + myList.length + " rows and " + myList[0].length + " columns: ");
        for (int i = 0; i < myList.length; i++){
          for (int j = 0; j < myList[0].length; j++){
              myList[i][j] = input.nextDouble();
          }
        }

    }

    public void getInput(double[][] userList) {



        System.out.println("You Entered:");
        for (int i = 0; i < userList.length; i++) {
            for (int j = 0; j < userList[0].length; j++) {

                // chars are just ints!
                System.out.print(userList[i][j] + " ");
            }

            // every row
            System.out.print("\n");
        }

        System.out.println("\n The sums are:");

        for (int column = 0; column < userList[0].length; column++) {
              double total = 0.0;

              for (int row = 0; row < userList.length; row++){
                  // sum column
                  total += userList[row][column];
              }

              System.out.print(total + " ");
        }

        // space for formating
         System.out.print("\n");
    }
}

This is what happens instead:

Enter 1 Random 2D Chars 
Enter 2 Sum Columns
Enter 3 Identical Arrays
Any other input will exit2
You Selected Sum Columns
Enter 3 rows and 4 columns: 
1 2 3 4
5 6 7 8
9.1 10.2 11.3 12.9
You Entered:
0.0 0.0 0.0 0.0 
0.0 0.0 0.0 0.0 
0.0 0.0 0.0 0.0 

 The sums are:
0.0 0.0 0.0 0.0

Now I have the opposite problem of the last post. Everything formats correctly, but it doesn't calculate properly. This is my only problem with the entire code.

Misa Lazovic · Accepted Answer · 2016-04-10 15:37:44Z

2

Well, you are first instantiating 2 empty arrays, then writing to one array and finally reading from second one (which is empty - actually filled with default double values, which is 0.0).
Basically, instead of:

double[][] myList = new double[3][4];
double[][] userList = new double[3][4];

feature2 f2 = new feature2();

f2.run(myList, input);

f2.getInput(userList);

try with:

double[][] myList = new double[3][4];

feature2 f2 = new feature2();

f2.run(myList, input);

f2.getInput(myList);

answered Apr 10, 2016 at 15:37

Misa Lazovic

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JB Nizet · Accepted Answer · 2016-04-10 15:38:27Z

2

You're asking the user to fill an array, and then displaying that array. So you need only one array, right?

Yet you have two arrays in your code: myList, which is filled by the user, and userList, which is displayed.

double[][] myList = new double[3][4];
double[][] userList = new double[3][4];

feature2 f2 = new feature2();

// ask the user to fill myList
f2.run(myList, input);

// but display userList
f2.getInput(userList);

Note that your naming is very confusing. The method which gets the input from the user is named run(), and the user which displays the array is named... getInput().

answered Apr 10, 2016 at 15:38

JB Nizet

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