finding incoming string field in dto object is of format MMYYYY

Hello,

I am just a beginner of Visual C#.

I have dto object which has loaded data from excel file into memory. 

It has several fields such as Course name(string) and Course Date(MMYYYY format) as string.

I need to check if the incoming  Course date field  is in the format MMYYYY

if it is not in that format, then i need to return error message

else return no error..Please advice. The code should be in C#...

Thanks

gs