[suresk]

I think a lot depends on the context, the job, and the languages involved.

Of course there is a trivial solution in pretty much any language, for example something like str(Decimal(x) + 1) in python. That's dead-simple and anyone should be able to do at least that.

The later addendum that they want someone to know how data is store by the computer seems to imply that they want an answer that doesn't use these conversions, which gets a lot trickier depending on the context. I think you'd still expect someone who does C/C++ work to get there pretty quickly, but it is more than 15 seconds - you have to think about some corner cases and how you handle the string having to be resized in some situations.

But in some languages, it isn't obvious to me how you'd do it (especially since strings are immutable in many languages) and I think it is maybe a bit unfair to ask someone who does Java or Python or whatever to do it off the top of their head.