\name{NumericConstants}
\alias{NumericConstants}
\title{Numeric Constants}
\description{
  How \R parses numeric constants.
}
\details{
  \R parses numeric constants in its input in a very similar way to C
  floating-point constants.

  \code{\link{Inf}} and \code{\link{NaN}} are numeric constants.  All
  other numeric constants start with a digit or period.

  Hexadecimal constants start with \code{0x} or \code{0X} followed by
  a non-empty sequence from \code{0-9 a-f A-F} which is interpreted as a
  hexadecimal number.

  Decimal constants consists of a nonempty 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.

  A numeric constant immediately followed by \code{i} is regarded as an
  imaginary \link{complex} number.

  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 part of numeric constant but
  a unary operator applied to the constant.
}
\seealso{
  \code{\link{Syntax}}.
  
  \code{\link{Quotes}} for the parsing of character constants,
}
\keyword{documentation}