Whats wrong with this for loop?

whats the problem with the following code, its giving me tough time for almost half a day.

if ((extImage != null))
                    {
                        string[] ast_url = null;
                        ast_url[0] = "";
                        ast_url[1] = "";
                        ast_url[2] = "";
                        ast_url[3] = "";
                        ast_url[4] = "";

                        for (int i = 0; i < 5; i++)
                        {
                            if (extImage[i] != null)
                            {
                                asset link = extImage[i];
                                ast_url[i] = link.url;
                            }
                        }

Re: Whats wrong with this for loop?

Is it not compiling or is it not producing the correct result? It it hanging?

Re: Whats wrong with this for loop?

its giving the following error

Object reference not set to an instance of an object.

When I remove the empty string assignments, then it gives another error of object refernce not set to an instance of an object

Re: Whats wrong with this for loop?

Change:

string[] ast_url = null;

to

string[] ast_url = new string[5];