Developer here. Modern C++ uses a single quotation mark as a separator.
Not that long numbers in any base are readable. They are just strings of characters to a human. If you insist on displaying the number as a whole then I'd suggest using a fixed width font. Then the user can just compare the length and look for the first differing digit when comparing ...
How is it useful to display this information? What is the context, can you give us a little bit more information?
Use abbreviation for large numbers: Names of large numbers
If you want to display a string of code, depending on the users need, you can:
a) Truncate the string
b) Truncate the string and show it on rollover (progressive disclosure)