Such strings are a non-empty sequence of decimal digits with an optional occurrence of a point (.) somewhere, and followed by an optional exponent. Either the point or the exponent must occur. The exponent starts with e or E, then there is an optional sign (+, -), and finally a non-empty sequence of decimal digits. Floating point numbers have an optional suffix to specify the precision: float (f, F), double (no suffix), or long double (l, L).