What's the difference between array[][] and array[,]?

Question

Can someone explain the difference between these two declarations?

double dArray[][];
double dArray[,];

@user: I'm not @BrokenGlass, but unlike in C and Java, in C# you need to declare the type as double[][] and double[,] as opposed to placing the brackets on the variable name. — BoltClock
– BoltClock, Commented Mar 1, 2011 at 2:54

Bala R · Accepted Answer · 2011-03-01 02:47:25Z

7

double dArray[][];

is Array-of-arrays while

double dArray[,];

is a two dimentional array.

it's easy enough to look them up.

MSDN Reference link

answered Mar 1, 2011 at 2:47

Bala R

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Ritch Melton · Accepted Answer · 2011-03-01 02:51:59Z

3

The last syntax is easy, it declares a multidimensional array of doubles. Imagine the array is 3x2, then there would be 6 doubles in the array.

The 1st syntax declares a jagged array. The second syntax is rectangular or square, but this syntax need not be. You could have three rows, followed by 3 columns, then 2 columns, then 1 column, ie: its jagged.

2nd: 1-1, 1-2, 1-3
     2-1, 2-2, 2-3

1st: 1-1, 1-2, 1-3
     2-1, 2-2,
     3-1,

answered Mar 1, 2011 at 2:51

Ritch Melton

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Marlon · Accepted Answer · 2011-03-01 03:06:03Z

The first is an array of double arrays, meaning each separate element in dArray can contain a different number of doubles depending on the length of the array.

double[][] dArray = new double[3][];
dArray[0] = new double[3];
dArray[1] = new double[2];
dArray[2] = new double[4];

           Index
        0       1       2
      -----   -----   -----
L  1  |   |   |   |   |   |
e     -----   -----   -----
n  2  |   |   |   |   |   |
g     -----   -----   -----
t  3  |   |           |   |
h     -----           -----
   4                  |   |
                      -----

The second is called a multidimensional array, and can be thought of as a matrix, like rows and columns.

double[,] dArray = new dArray[3, 3];

         Column
        0   1   2
      -------------
   0  |   |   |   |
R     -------------
o  1  |   |   |   |
w     -------------
   2  |   |   |   |
      -------------

user541686 · Accepted Answer · 2011-03-01 02:48:26Z

1

See the official documentation (click on the C# tab).

answered Mar 1, 2011 at 2:48

user541686

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