Date format issue in C#

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C#

C#4.0

ASP.NET4

I have a Date in excel sheet, i'm try to load the date into string object.
Here when i try to load the date into page itself then i want to check the condition if the date format is "dd-MMM-yy", then display correct date other wise error message.

EX:

string date="11-Feb-13";

if(date is "dd-MMM-yy")
//insertion
else
//error message

Here i'm confusing about the highlited one.How can i check that if condition any help regarding this issue...