Sum of 3x3 in 2D-Array

Question

Write a program in java that read two 3 by 3 matrix and find out their sum and display result?

i tried this but i got Runtime error

Scanner r=new Scanner(System.in);
   int [][]array = null;
    int[][]array2 = null;
  int total=0;
  System.out.println("Enter matrix");
  for(int row=0;row<array.length;row++){
      for(int col=0;col<array[row].length;col++){
             array[row][col]=r.nextInt();

             array[row][col]=r.nextInt()

;

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

      total=array[row][col]+array2[row][col];
        System.out.println("   ");

Answer 1

You are not allocating any memory for the array references, they are referencing nothing(null)... Try:

int[][] array = new int[3][3];
int[][] array2 = new int[3][3];

Also, you are missing a semi-colon in 9th line of your code.Also,in same line, I believe it should be array2 & not array.

Answer 2

The first FOR-Loop demonstrates how to input values in the arrays. This code will require that the user inputs the values of both arrays simultaneously.

The second FOR-Loop demonstrates how to sum the values of each array. Later, both arrays are added together.

    //Since you know the the array will be 3x3,
    //declare it!
    int[][] array1 = new int[3][3];
    int[][] array2 = new int[3][3];

    int array1Total = 0;
    int array2Total = 0;
    int endResult;

    for (int x = 0; x < array1.length; x++) {

        for (int y = 0; y < array1[x].length; y++) {

            array1[x][y] = r.nextInt();
            array2[x][y] = r.nextInt();

        }
    }

    for (int x = 0; x < array1.length; x++) {

        for (int y = 0; y < array1[x].length; y++) {

            array1Total += array1[x][y];
            array2Total += array2[x][y];

        }
    }

    endResult = array1Total + array2Total;