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% File src/library/base/man/NumericConstants.Rd

% Part of the R package, https://www.R-project.org

% Copyright 1995-2015 R Core Team

% Distributed under GPL 2 or later

\name{NumericConstants}

\alias{NumericConstants}

\alias{1L}

\alias{0x1}

\alias{1i}

\title{Numeric Constants}

\description{

  How \R parses numeric constants.

}

\details{

  \R parses numeric constants in its input in a very similar way to C99

  floating-point constants.

  \code{\link{Inf}} and \code{\link{NaN}} are numeric constants (with

  \code{\link{typeof}(.) "double"}).  In text input (e.g., in

  \code{\link{scan}} and \code{\link{as.double}}), these are recognized

  ignoring case as is \code{infinity} as an alternative to \code{Inf}.

  \code{\link{NA_real_}} and \code{\link{NA_integer_}} are constants of

  types \code{"double"} and \code{"integer"} representing missing

  values.  All other numeric constants start with a digit or period and

  are either a decimal or hexadecimal constant optionally followed by

  \code{L}.

  Hexadecimal constants start with \samp{0x} or \samp{0X} followed by

  a non-empty sequence from \samp{0-9 a-f A-F .} which is interpreted as a

  hexadecimal number, optionally followed by a binary exponent.  A binary

  exponent consists of a \code{P} or \code{p} followed by an optional

  plus or minus sign followed by a non-empty sequence of (decimal)

  digits, and indicates multiplication by a power of two.  Thus

  \code{0x123p456} is \eqn{291 \times 2^{456}}{291 * 2^456}.

  Decimal constants consist of a non-empty sequence of digits possibly

  containing a period (the decimal point), optionally followed by a

  decimal exponent.  A decimal exponent consists of an \code{E} or

  \code{e} followed by an optional plus or minus sign followed by a

  non-empty sequence of digits, and indicates multiplication by a power

  of ten.

  Values which are too large or too small to be representable will

  overflow to \code{Inf} or underflow to \code{0.0}.

  A numeric constant immediately followed by \code{i} is regarded as an

  imaginary \link{complex} number.

  A numeric constant immediately followed by \code{L} is regarded as an

  \code{\link{integer}} number when possible (and with a warning if it

  contains a \code{"."}).

  Only the ASCII digits 0--9 are recognized as digits, even in languages

  which have other representations of digits.  The \sQuote{decimal

    separator} is always a period and never a comma.

  Note that a leading plus or minus is not regarded by the parser as

  part of a numeric constant but as a unary operator applied to the constant.

}

\note{

  When a string is parsed to input a numeric constant, the number may or

  may not be representable exactly in the C double type used.  If not

  one of the nearest representable numbers will be returned.

  \R's own C code is used to convert constants to binary numbers, so the

  effect can be expected to be the same on all platforms implementing

  full \abbr{IEC} 60559 arithmetic (the most likely area of difference being

  the handling of numbers less than \code{\link{.Machine}$double.xmin}).

  The same code is used by \code{\link{scan}}.

}

\seealso{

  \code{\link{Syntax}}.

  For complex numbers, see \code{\link{complex}}.

  \code{\link{Quotes}} for the parsing of character constants,

  \code{\link{Reserved}} for the \dQuote{reserved words} in \R{}.

}

\examples{

## You can create numbers using fixed or scientific formatting.

2.1

2.1e10

-2.1E-10

## The resulting objects have class numeric and type double.

class(2.1)

typeof(2.1)

## This holds even if what you typed looked like an integer.

class(2)

typeof(2)

## If you actually wanted integers, use an "L" suffix.

class(2L)

typeof(2L)

## These are equal but not identical

2 == 2L

identical(2, 2L)

## You can write numbers between 0 and 1 without a leading "0"

## (but typically this makes code harder to read)

.1234

sqrt(1i) # remember elementary math?

utils::str(0xA0)

identical(1L, as.integer(1))

## You can combine the "0x" prefix with the "L" suffix :

identical(0xFL, as.integer(15))

}

\keyword{documentation}