Your code is a mess of cascading conversions, you need to check that every conversion works as expected, use the debugger to do so.
are BigInteger, and you want
TenBase = ToTenBase(BigValue, 3)
see what you do with ToTenBase
ToTenBase does BigValue as BigInteger => ToString => ToCharArray => ToString => ToBigInteger => ToString => ToBigInteger
advice: you have BigInteger, you want BigInteger, stay BigInteger.
There is a rather simple way to extract digits from a number without convertion to string
BI = 22222222210222211011111222011100022001111
Un = BI % 10 = 1
Tn = BI / 10 = 2222222221022221101111122201110002200111
repeat operation for each digit you need.
There is a tool that allow you to see what your code is doing, its name is debugger
. It is also a great learning tool because it show you reality and you can see which expectation match reality.
When you don't understand what your code is doing or why it does what it does, the answer is debugger
Use the debugger to see what your code is doing. Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.
Debugger - Wikipedia, the free encyclopedia
Visual Basic / Visual Studio Video Tutorial - Basic Debugging - YouTube
Visual Basic .NET programming for Beginners - Breakpoints and Debugging Tools
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't find bugs, it just help you to. When the code don't do what is expected, you are close to a bug.