I understand your requirement like this :
- You have allways a string which only contains numbers.
- You allways want to have the last 2 numbers of the string as decimals.
So your code could look like this :
string s = "000000099";
int i = (int)s;
double d = (double)i / 100;
string s2 = d.ToString("0.00");
I have done it in steps so you could see how it works.
The code itself could be compressed ...