chnage date from "22-12-2012" to "12-22-2012"

First of all, I don't think you really need to "convert". You should not work with string representation of data instead of data. In your case, you should work with System.DateTime instead of strings representing it. Only of you need to show the data on screen, you use one of System.DateTime methods, and only then you choose the format. Please see:
http://msdn.microsoft.com/en-us/library/system.datetime.aspx[^], read on every ToString method.

For formatting, please see
http://msdn.microsoft.com/en-us/library/az4se3k1.aspx[^],
http://msdn.microsoft.com/en-us/library/8kb3ddd4.aspx[^].

Another way of formatting is through choosing appropriate culture, see, for example:
http://msdn.microsoft.com/en-us/library/ht77y576.aspx[^].

In rare cases, you need to interpret string from certain format. Even this can be simplified, because, say, in SQL you should better use DATE type not tied to a particular format, in contrast to strings. But in case you need, you should parse a string into System.DateTime, so see all the methods Parse, ParseExact, TryParse and TryParseExact.

Of course, using the methods referenced, you can "convert" as you wanted, but "convert" approach is wrong.

—SA

DateTime _date = Convert.ToDateTime("22-12-2012");
string str = _date.ToString("MM-dd-yyyy");

Convert your date like below

string date=yourDate.ToString("MM-DD-YYYY");

you can change the date format whatever you want.
Hope this helps

Try this :-

DateTime shortDate = new DateTime();

               System.Globalization.DateTimeFormatInfo dtfi = new                                                                           System.Globalization.DateTimeFormatInfo();

           dtfi.ShortDatePattern = "MM-dd-yyyy";

           shortDate = DateTime.ParseExact(yourDate, "d", dtfi);

Thanks