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C++ Floating-Point Constants

Floating-point constants specify values that must have a fractional part. These values contain decimal points (.) and can contain exponents.


floating-constant :
fractional-constant exponent-partopt floating-suffixopt
digit-sequence exponent-part floating-suffixopt
fractional-constant :
digit-sequenceopt . digit-sequence
digit-sequence .
exponent-part :
e signopt digit-sequence
E signopt digit-sequence
sign : one of
digit-sequence :
digit-sequence digit
floating-suffix :one of
f l F L

Floating-point constants have a "mantissa," which specifies the value of the number, an "exponent," which specifies the magnitude of the number, and an optional suffix that specifies the constant's type. The mantissa is specified as a sequence of digits followed by a period, followed by an optional sequence of digits representing the fractional part of the number. For example:


The exponent, if present, specifies the magnitude of the number as a power of 10, as shown in the following example:

18.46e0      // 18.46
18.46e1      // 184.6

If an exponent is present, the trailing decimal point is unnecessary in whole numbers such as 18E0.

Floating-point constants default to type double. By using the suffixes f or l (or F or L — the suffix is not case sensitive), the constant can be specified as float or long double, respectively.

Although long double and double have the same representation, they are not the same type. For example, you can have overloaded functions like

void func( double );


void func( long double );

See Also