if List contains is null

Question

Hi all If I want to say history list was null matrix [][] be 0 How could be written? the code blew gives an error. List > history = new List >() ; int [][] matrix= new int[5][]; if (history[y].Contains(192.168.2.160 StringComparer.OrdinalIgnoreCase)) matrix[x+4][y] = 1; else if (history[y].Contains==null) matrix[x][y] = 0; thanks

Vulpes · Answer

Can I just check that you know how to fully initialize a two dimensional 'jagged' array. This line on its own is not sufficient - it just tells the compiler than there are 5 single dimensional arrays within the jagged array. int [][] matrix= new int[5][]; You have to initialize each of the 5 single dimensional arrays individually as they can be of different lengths. So if you want the array at index x of the jagged array to be of length 5 you'd do: matrix[x] = new int[5];

diamond diamond · Answer

Thanks Vulpes I correct it with this style int [] matrix=new int [51000]

diamond diamond · Answer

Vulpes I want to create matrix which has 5 rows and history.count columns. for that as far as I know it is sufficient to write is it wrong? Can you let me know how do I do for that?

diamond diamond · Answer

Vulpes int [][] matrix= new int[5][]; The exception message is as same as already message check to determined if the object is null before calling the method {Object reference not set to an instance of an object.}

Vulpes · Answer

What exception are you getting? Have you initialized matrix[x] somewhere? matrix[x] = new int[5]; // or whatever

diamond diamond · Answer

Many thanks But this time for matrix[x][y] = 0; gives an exception ??!!!

Vulpes · Answer

If you're wanting to check whether the element of history at index y is either an empty List or null you can use: else if (history[y] == null || history[y].Count == 0) Note that it's not possible for a List 's Count property to be less than 0.

diamond diamond · Answer

Thanks an error is solved but code is not suitable for this work I used history[].count this time is run but the command of if gives an exception: else if (history[y].Count matrix[x][y] = 0; check to determined if the object is null before calling the method {Object reference not set to an instance of an object.}

Vulpes · Answer

If you want to test that the element of history at index y is null then it's: else if (history[y] ==null) matrix[x][y] = 0; However if you want to test that the List object at index y of history contains a null value then it's: else if (history[y].Contains(null)) matrix[x][y] = 0;