Another problem arises when undefined values are read. When reading a zero for the denominator,
the value of the read fraction is not well defined. This problem is detected in the constructor of
the class Fraction that is invoked by the expression Fraction(n,d). However, handling inside
class Fraction means that a format error automatically results in an error handling of the class
Fraction. Because it is common practice to record format errors in the stream, it might be better to
set ios_base::failbit in this case.