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Thread: Problems getting value of index in 2D array operation

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    Junior Member Flcha's Avatar
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    Default Problems getting value of index in 2D array operation

    Before starting to tell the problem with my method, I want to greet everyone in Java community

    This time, I have a problem with an 2D array.
    Arr is of integer type with dimensions of [4][4].
    Let me display the code...
    ...
    public static void main(String args[]) {
      int[][]arr = new int[4][4];
        int size=0;
    for (int i = 0; i < size; i++) {
        for (int j = 0; j < size; j++) {
            arr[i][j] = size * j + i;
    IO.outputln("result is: "+arr[i]+arr[j]);
        }
    }
    }

    I would like to know the value stored in arr[1][3] after executing the code above.
    I can't see the value in the console. What is missing ?


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    Default Re: Problems getting value of index in 2D array operation

    What result are you getting? Copy and post the console from a sample run.

    You've used the 'size' variable before (I think), and you shouldn't be. That's what you're missing in this case. Post your corrected code, and then I'll show you a better way.

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    Junior Member Flcha's Avatar
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    Default Re: Problems getting value of index in 2D array operation

    Hi Greg.
    I can't tell you the result of the operation, because the terminal window doesn't show me anything.
    About the variable size, I don't know. I just copied this small line of code from my teacher example to create a better understanding program with an output result ^^

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    Default Re: Problems getting value of index in 2D array operation

    That you're seeing nothing in the terminal window is the result, and it's significant.

    Trace the code - keep track of the variable values with pencil and paper if you need to - and determine what will happen at the for loops with size set to 0.

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    Junior Member Flcha's Avatar
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    Default Re: Problems getting value of index in 2D array operation

    I used the breakpoint and when it arrives to the step of the "For loop" it jumps to the end of the program...
    If I change size=4. the terminal window will display 16 results

    Now I can tell what is the value of arr[1][3]

    Thanks for the tip once again. the variable is the problem
    Last edited by Flcha; July 25th, 2014 at 05:56 PM.

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    Default Re: Problems getting value of index in 2D array operation

    Glad you figured it out. As I said earlier, the code below demonstrates a more appropriate way to write for() loops to iterate arrays.
    // a method to demonstrate the declaration and initialization
    // of a 2D array with 4 rows and 4 columns. the first element of
    // each row of the array is initialized to the row number, and
    // each element in the row thereafter increases by one
    public static void arrayMethod()
    {
        // declare a 2D array with 4 rows and 4 columns
        int[][] arr = new int[4][4];
     
        // initialize the array
        // for each row, i: arr.length = number of rows
        for (int i = 0 ; i < arr.length ; i++)
        {
            // for each column, j: arr[i].length = the number of
            // elements or columns in the row i
            for (int j = 0 ; j < arr[i].length ; j++)
            {
                arr[i][j] = j + i;
            }
        }
     
        // display the completed array
        System.out.println( Arrays.deepToString( arr ) );
     
    } // end method arrayMethod()

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