As was pointed out, helper functions are your friend or even just overloading functions to return different types depending on your needs.

Remember! More code just takes up more memory, which is very plentiful these days, if anything you only want to be worried about usability and performance on critical sections, so if something seems messy, write more code(to an extent anyway.)

That or write cleaner feeling code.

value = 0; //valid
value = 's';//invalid

I see a problem with these two lines. How do you have a class that accepts 0 (an int) and rejects 's' (an int)?

's' is a char in C++, so you'd need a function that takes a char and produces an error when passed something other than a digit. Or just always produces an error.

Ah, you're right. Character constants became of char type in C++. My mistake.

Yep, it's one of the subtle differences between C and C++. It means that code like this will have different results in the two languages.

int main(){
  return sizeof('a');
}