What are the differences between using int[][] and int[,]? [duplicate]

Answer 1

int[][] is a jagged array, where int[,] is a two dimensional array.

plainly

var a = int[][]

allows you do have an array like this:

a[0] = new int[2];
a[1] = new int[5];

where as with int[,] you must always have the second portion of the array be the same:

var a = int[2,2];

a[0,0]
a[0,1]
a[1,0]
a[1,1]

you can't have a[2,2];

Answer 2

int[][] is called an array of arrays, it can have arbitrary length for each row.

int[,] is called rectangular array, where all the rows have the same length. it Can be simulated by the first one.

Answer 3

Here's an excellent article about arrays, covering this topic very well.