How to encode and decode my string using base-62 in C#.net (.net framework 3.5)?

How to encode and decode my string using base-62 in C#.net (.net framework
3.5)?

I want to encode and decode my string using base-62 in C#.net with .net
framework 3.5. I referred this link http://trycatch.me/counting-in-base62/
In the above link, the decoded ouput return value is long, but i want my
decoded output value as string,So that i can verify my original string and
decoded output string as same or not.
I want my encoded value length is smaller than the original string. E.x:
original string =a12346 And some Encoded junk value like Mm77 .(For URL
Shortening)
Can i get any links to achieve this task??