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Thread: help 2d array confusion

  1. #1
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    Default help 2d array confusion

    int [] [] matrix = {
        {16, 3, 2, 13},
        {5, 10, 11, 8},
        {2, 6, 7, 12},
        {2, 15, 14, 1}
    };
     
     
     
    result = 0;
    for(row = 3 ; row > 3; row--){
        result = matrix[row][row] +result;
            }
    sumDiag2 = result;
    if (sumDiag2 == magic){
         System.out.println("Minor Diagonal  = "+ result +  "  OK");}
    else
        System.out.println("Minor Diagonal = "+ result + "  NOT OK");
     
     
        }
    }

    ok so i have this code i want to add the minor diagonals which should be 32 (13,11,6,2)
    but i keep getting 0... i dont get it help


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    Default Re: help 2d array confusion

    for(row = 3 ; row > 3; row--){
        result = matrix[row][row] +result;
            }

    This will never go through the for loop as row is already 3, which means that it already is not greater than 3.

    That might be part of the problem.

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    Default Re: help 2d array confusion

    So result will still be 0?

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    Default Re: help 2d array confusion

    result = 0;
    for(row = 3 ; row >= 0; row--){
        result = matrix[row][row] +result;
            }
    sumDiag2 = result;
    if (sumDiag2 == magic){
         System.out.println("Minor Diagonal  = "+ sumDiag2 +  "  OK");}
    else
        System.out.println("Minor Diagonal = "+ sumDiag2 + "  NOT OK");

    oh darn i overlooked sorry so i changed it to row >= 0
    now it just displays 34 when it supposed to display 32

    i dont understand its supposed to add
    matrix[3][3] because the value of row starts at 3
    but it keeps computing the value of the major diagonal (matrix[0][0])

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    Default Re: help 2d array confusion

    for(row = 3 ; row >= 0; row--){
    result = matrix[row][row] +result;
    }

    First iteration x = 3
    result = matrix[3][3];
    Second iteration x = 2
    result = matrix[3][3] + matrix[2][2];
    Third iteration x = 1
    result = matrix[3][3]+ matrix[2][2] + matrix[1][1];
    Fourth iteration x = 0;
    result = matrix[3][3] + matrix[2][2] + matrix[1][1] + matrix[0][0];

    So result should be

    1 + 7 + 10 + 16
    = 34

    I could think that perhaps an array of results


    result[0] = matrix[3][3];
    result[1]= result[0] + matrix[2][2];
    result[2] = result[1] + matrix[1][1];
    result[3] = result[2] + matrix[0][0];

    for (int x = 0; x < =3; x++)
    {
    if (x ==0)
    result[x] = matrix[3-x][3-x];
     
    else
    {
    result[x] = result[x-1] + matrix[3-x][3-x];
    }
    }

    Now check if result[3] = magic.

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