"Can you help me?" may be indicative of an unanswerable question, but it is not necessary so.
People often seem to be blinded by the "ask an (actual) question" mentality and downvote and close perfectly appropriate questions that only have some less-than-ideal phrasing.
In many cases, it's trivial to convert a "Can you help me?" question into an "actual" question (whether that question would be appropriate is a different issue).
Taking your example:
I'm trying to convert a string to a number. Can anyone help me?
versus
How do I convert a string to a number?
The asker appears to want exactly the same thing in each case, the phrasing is just a little different.
Even if there isn't such an easy fix, it's often easy to see what the asker wants and add an "actual" question (although not necessarily an appropriate one, of course).
If it's really easy to "fix" with an edit (which I often do), it's definitely not something you should be downvoting or closing a question over.
Be optimistic. Try your best to see what the asker wants and edit the question into something appropriate, if at all possible.
To this end, I also propose we favour actually explaining what's wrong with the question as a whole as opposed to fixating on "Can you help me". For example, if someone says:
I can't get the correct answer with my code. Can you help me?
with no description of the output or any errors, one can also get rid of "Can you help me" as described above, although the end result is still a terrible question:
How do I get the correct answer with my code?
A much better comment in such cases would be:
Do you get any errors when trying to compile or run your code? If yes, can you post the exact error message? If no, what output are you getting? Can you also post the output you're expecting?
Alternatively or additionally, simply close it using the "debugging help" close reason.
Simply linking here DOES NOT HELP - at best it gives some vague guidelines for what a good question should look like (which can be found in the help center as well), where concrete guidance specific to their situation would be much more beneficial to them (in my opinion). They'll probably ignore it anyway, but there's presumably a slightly greater chance that they won't.