Problems declaring a 2 dimensional array

Jagged array [][]

If using an array of type int[][] (a jagged array) you want to be initialise your arrays like this:

public int[] _SpDep = new int[50];
public int[][] _SpDepCnt = new int[50][];
public int[][] _SpReadType = new int[50][];

And then initialise the arrays inside the array:

var length = 20;
for (int i = 0; i < length; i++)
{
    _SpDepCnt[i] = new int[length];
     _SpReadType[i] = new int[length];
}

It is called a jagged array because the lengths of the second part can vary, you could have this for example:

[1,2,3,4]
[5,6]
[7,8,9]

Multidimensional array [,]

I believe you want to use the type int[,] which is called a multidimensional array. They make an array with two fixed dimensions.

public int[,] _SpDepCnt = new int[50, 20];
public int[][] _SpReadType = new int[50, 20];

Multidimensional arrays will create the same sized array for each index:

[1,2,3]
[4,5,6]
[7,8,9]

When you declare an "array of arrays" using [][], you need to initialise the outer dimension to reference allocated arrays, like this:

public int[][] _SpReadType = new int[50][];

for (int i = 0; i < 50; ++i)
    _SpReadType[i] = new int[SIZE]; // Where you have to decide on SIZE

The [][] arrays are also known as "ragged arrays" or "jagged arrays" because the size of each row can be different, since each row is a separate array.

Alternatively, you can use actual 2D arrays using this syntax: [,]

For example:

public int[,] _SpReadType = new int[50,SIZE];

Then you access the elements like so:

int value = _SpReadType[row,col];

that's a jagged array you have to initialize the element before you can use it

myJaggedArray[0] = new int[5];
myJaggedArray[1] = new int[4];
myJaggedArray[2] = new int[2];

http://msdn.microsoft.com/en-us/library/2s05feca(v=vs.71).aspx

What you tried is called jagged arrays, not multidimensional arrays.

If you want to use 2 dimennsional array, you can use it like;

 public int[,] _SpDepCnt = new int[50, 50];
 _SpDepCnt[_DepNo, _CntNo] = 1;

If you want to use jagged array, you can use it like;

public int[][] _SpReadType = new int[50][];

for (int i = 0; i < 50; i++)
    _SpReadType[i] = new int[SIZE]; 

A jagged array is an array whose elements are arrays. The elements of a jagged array can be of different dimensions and sizes. A jagged array is sometimes called an "array of arrays."

You must reserve memory for the 2D-Array

public int[][] _SpDepCnt = new int[50][];
_SpDepCnt[_DepNo] = new int[50];
_SpDepCnt[_DepNo][_CntNo] = 1;