Writing a for loop for a 2d Array?

Question

I've got a program where the user is giving the program the size of the array ie(the column and row size) and I am trying to give every position in the array the same value. I'm having an issue with my loop though, here it is.

for(int i = 0; i < row; i++){
        for(int j = 0; j < col; j++){
            //CODE
        }   
    }

I can see that the issue is I am trying to give a value to a position that doesn't exist but I have no idea how to work around this issue. Any help would be appreciated :)

Before assign the value you need to allocate memory for the array. — Alejandro Alcalde
– Alejandro Alcalde, Commented May 20, 2014 at 8:13

Dmitrii Bychenko · Accepted Answer · 2014-05-20 08:27:44Z

1

Try working with length, not with user input:

  // ask user for sizes
  int col = ...;
  int row = ...;

  // declare the array, let it be of type int 
  // it's the last occurence of "row" and "col"
  int[][] data = new int[row][col];

  // loop the array    
  for (int r = 0; r < data.length; ++r) { // <- not "row"!
    int[] line = data[r];

    for (int c = 0; c < line.length; ++c) { // <- not "col"!
      // do what you want with line[c], e.g. 
      // line[c] = 7; // <- sets all array's items to 7
    }
  }

working with actual array's dimensions just prevent you from accessing non-existing items

edited May 20, 2014 at 8:27

answered May 20, 2014 at 8:22

Dmitrii Bychenko

188k20 gold badges178 silver badges231 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Dénes Varga · Accepted Answer · 2014-05-20 08:15:35Z

0

From the code snippet you provided it seems you are fine. Maybe the array is not well initialized or you mismatched the row and column numbers. Try to use more specific variable names than 'i' and 'j'.

answered May 20, 2014 at 8:15

Dénes Varga

1

Comments

Macrosoft-Dev · Accepted Answer · 2014-05-20 08:16:24Z

0

in java

try{
  for(int i = 0; i < row; i++){
        for(int j = 0; j < col; j++){
            //CODE
        }   
    }
}catch(IndexOutOfBoundsException exp){
   System.out.printlv(exp.getMessage());
}

answered May 20, 2014 at 8:16

Macrosoft-Dev

2,1851 gold badge13 silver badges15 bronze badges

Comments

Andy · Accepted Answer · 2014-05-20 08:18:26Z

0

To begin, what makes you say that you "can see that the issue is I am trying to give a value to a position that doesn't exist"? What symptoms are you seeing that makes you believe this?

On the face of it, your code looks fine, however (and this is a big however) you have omitted the most important bits of code, viz the declaration of your 2D array, and the part inside the loop body where you assign the value to the array member. If you add these then I, or somebody else, may be able to help further.

answered May 20, 2014 at 8:18

Andy

5791 gold badge6 silver badges21 bronze badges

4 Comments

user3655586 Over a year ago

My program only throws the exception, Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 5 if I have two uneven inputs into the program. ie cols is 5 and row is 6.

user3655586 Over a year ago

So from what I can tell its looping over and trying the add a value to the position of [5][5] for example which doesn't exist...?

Andy Over a year ago

Go on, be a hero and give us the whole bit of code :-) From this exception, it looks like you're either: 1) Declared the array too small; 2) Got incorrect values for 'row' or 'col', or 3) Used the wrong indices in your assignment (a common error is to have them the wrong way around). You'd really make life a lot easier for us if you gave the code though. This isn;t meant to be a guessing game and you are uiung people's valuable time.

Andy Over a year ago

So if it works when row and col are the same, then it sounds like you are using them the wrong way around in your assignment.

Erik Lucio · Accepted Answer · 2014-05-20 08:25:12Z

0

Solution:

int matriz[][] = new int [row][col];
for(int i = 0; i <row; i++){
    for(int j = 0; j < col; j++){
        matriz[i][j] = 0; 
    }   
}

edited May 20, 2014 at 8:25

answered May 20, 2014 at 8:20

Erik Lucio

9487 silver badges8 bronze badges

Comments

Debasis Mondal · Accepted Answer · 2014-05-20 09:13:50Z

0

//try this one 
import java.util.Scanner;  //Scanner class required for user input.

class xyz
{
  public static void main(String ar[])
  {
     int row,col;
     Scanner in=new Scanner(System.in); //defining Object for scanner class
     System.out.println("Enter row");
     row=in.nextInt();
     System.out.println("Enter Column");
     col=in.nextInt();
     int mat[][]=new int[row][col];    //giving matrix size
     for(int i=0;i<row;i++)
     {
        for(int j=0;j<col;j++)
        {
            mat[i][j]=0;   //or any value decided by you
        }
     }
  }
}

answered May 20, 2014 at 9:13

Debasis Mondal

658 bronze badges

Collectives™ on Stack Overflow

Writing a for loop for a 2d Array?

6 Answers 6

Comments

Comments

Comments

4 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

6 Answers 6

Comments

Comments

Comments

4 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related