Something is going wrong while placing values into array, Sum of arrays

Question

Basically, the program given to me is to add the sum of the array's rows and columns and give it back into the same array

if m = 3 , n = 4

Eg:

3 4 5 6 18

1 2 3 4 10

4 3 3 2 12

8 9 11 12

(The last 12 is the sum of 6 + 4 +2)

So, this is the code for it

void summatrix()
    {
        for(int i=0;i<m-1;i++) // m - 1 because total array size is m but values only placed till m-1
        {
            int sum = 0;
            for(int j=0;j<n-1;j++)
            {
             sum += mat[i][j];
             mat[i][n] = sum; // Pretty sure the problem is here
            }
            System.out.println("Sum of "+ i + " " + (n) + " is "+ sum);

        }
        for(int j=0;j<n-1;j++) // n-1 beacuse total array size is n, values only placed till n-1
        {
            int sum=0;
            for(int i=0;i<m-1;i++)
            {
                sum+=mat[i][j];
                mat[m][j] = sum; // Pretty sure the problem is here
            }
            System.out.println("Sum of "+ (m) + " " + j + " is "+ sum);

        }
        show_mat(); // prints the array

Input and output :

    The matrix is : 
1 2 3 0 
1 2 3 0 
1 2 3 0 
0 0 0 0 
Sum of 0 4 is 6
Sum of 1 4 is 6
Sum of 2 4 is 6
Sum of 4 0 is 3
Sum of 4 1 is 6
Sum of 4 2 is 9
The matrix is : 
1 2 3 0 
1 2 3 0 
1 2 3 0 
0 0 0 0

My printing code:

 void show_mat()
    {
        System.out.println("The matrix is : ");
        for(int i=0;i<m;i++)
        {
            for(int j=0;j<n;j++)
            {
                System.out.print(mat[i][j] + " ");
            }
            System.out.println();
        }
    }

I can post all of my code or anymore whatever is needed if wanted. Sorry if my coding looks bad.. still relatively new to this.

@theSun `mat[i][n] = sum;` In this piece of code you are accessing `n`, which is out of bounds, since it's the size of the second dimension, maybe you mean `mat[i][n-1] = sum;` — nbro, Sep 05 '14 at 19:25
Put the "mat[i][n-1] = sum;" and "mat[m-1][j] = sum;" outside the inner for loop and inside the outer for loop. Your question is not clear. However I provided information on the basis of whatever you have here. — Ripu Daman, Sep 05 '14 at 19:25
@ripudam m-1 and n-1 have worked perfectly. Thanks yu very much. How can i mark you as correct answer? — sun, Sep 05 '14 at 19:28
What is the problem? Also did you see that I edited my comment? — Ripu Daman, Sep 05 '14 at 19:29
@ripudam I saw the edit, and i used the edited code. it works perfectly now. thank you! — sun, Sep 05 '14 at 19:30
@Usar Yes I realized after you posted as question wasn't clear do I just didn't realize that. — Ripu Daman, Sep 05 '14 at 19:30
@theSun Yes, at the beginning is very difficult not to do things wrong with the bounds of the arrays — nbro, Sep 05 '14 at 19:32
@ripudam Yes it is, How can i mark your answer as the correct answer? or increase your reputation? — sun, Sep 05 '14 at 19:33
I have added the suggestion as the answer. You can mark it as answer. — Ripu Daman, Sep 05 '14 at 19:33
@usar Thanks to you I now know how to fix my future array problems So thanks a lot :D — sun, Sep 05 '14 at 19:33
Use a debugger http://stackoverflow.com/questions/25385173/what-is-a-debugger-and-how-can-it-help-me-diagnose-problems — Raedwald, Sep 05 '14 at 21:38

score 0 · Accepted Answer · edited Sep 05 '14 at 19:48

0

Put the mat[i][n-1] = sum; and mat[m-1][j] = sum; outside the inner for loop and inside the outer for loop.

edited Sep 05 '14 at 19:48

nbro

15,395
32
113
196

answered Sep 05 '14 at 19:33

Ripu Daman

2,482
2
18
22

score 0 · Answer 2 · edited Sep 05 '14 at 20:01

0

In your inner loop you should set the value of your sum after the loop and only once. Something like this:

int sum = 0;
for(int j = 0; j < n-1; j++) {
    sum += mat[i][j];
}
mat[i][n-1] = sum;//n-1

edited Sep 05 '14 at 20:01

nbro

15,395
32
113
196

answered Sep 05 '14 at 19:34

Murat Erozlu

1

Please, notice that mat[i][n] goes out of bounds, so correct it with `mat[i][n-1]` – nbro Sep 05 '14 at 19:44

score 0 · Answer 3 · answered Sep 05 '14 at 19:42

Make sure that the cells to contain the row and column sum are zero before summing.

Try

package com.example.matrix;

public class MatrixOperation {

    public void summatrix(int[][] matrix) {
        int rows;
        int cols;

        rows = matrix.length;
        cols = matrix[0].length;
        // initialize sums
        for (int i=0; i < rows-1; i++) {
            matrix[i][cols-1] = 0;
        }
        for (int j=0; j < cols-1; j++) {
            matrix[rows-1][j] = 0;
        }

        for (int i=0; i < rows-1; i++) {
            for (int j=0; j < cols-1; j++) {
                matrix[rows-1][j] = matrix[rows-1][j]+matrix[i][j];
                matrix[i][cols-1] = matrix[i][cols-1] + matrix[i][j];
            }
        }


        for (int i=0; i < rows; i++) {
            for (int j=0; j < cols; j++) {
                System.out.print(matrix[i][j] + " ");
            }
            System.out.println("");
        }
    }
}

Something is going wrong while placing values into array, Sum of arrays

3 Answers3