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\name{read.and.check}
\alias{read.and.check}
\title{Read data interactively and check that it satisfies conditions}
\usage{
read.and.check(message = "", what = numeric(), lower, upper, answer.in,
default)
}
\arguments{
\item{message}{message displayed before prompting for user input.}
\item{what}{the type of \code{what} gives the type of data to be read.}
\item{lower}{lower limit of input, for numeric input only.}
\item{upper}{upper limit of input, for numeric input only.}
\item{answer.in}{the input must correspond to one of the elements of the
vector \code{answer.in}, if supplied.}
\item{default}{value assumed if user enters a blank line.}
}
\description{
Input is read interactively and checked against conditions specified
by the arguments \code{what}, \code{lower}, \code{upper} and
\code{answer.in}. If the input does not satisfy all the conditions,
an appropriate error message is produced and the user is prompted
to provide input. This process is repeated until a valid input value
is entered.
}
\value{
The value of the valid input. When the \code{default} argument is
specified, a blank line is accepted as valid input and in this case
\code{read.and.check} returns the value of \code{default}.
}
\note{
Since the function does not return a value until it receives valid
input, it extensively checks the conditions for consistency before
prompting the user for input. Inconsistent conditions will cause
an error.
}
\author{Martyn Plummer}
\keyword{utilities}
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