Repeat until the input is a number
Create a function
readNumber which prompts for a number until the visitor enters a valid numeric value.
The resulting value must be returned as a number.
The visitor can also stop the process by entering an empty line or pressing “CANCEL”. In that case, the function should return
The solution is a little bit more intricate that it could be because we need to handle
So we actually accept the input until it is a “regular number”. Both
null (cancel) and empty line also fit that condition, because in numeric form they are
After we stopped, we need to treat
null and empty line specially (return
null), because converting them to a number would return