Conditional Operations Error in R

Question

I am programming a simple recursive algorithm to compute the Fibonacci sequence in R, as I do in C. Follow the same below:

fibonacci <- function (n)
{
  if (n == 1L)
    return (0L)
  else if (n == 2L || n == 3L)
    return (1L)
  else
    return (fibonacci(n - 1L) + fibonacci(n - 2L))
} 

n <- readline(prompt="Insira um valor inteiro: ")
n <- as.integer(n)

print(fibonacci(n))

The script apparently runs smoothly in the Rstudio environment. But when running on the linux console, I get the following error:

Enter an integer value: Error in if (n == 1L) Return(0L) Else if (n == 2L || n == 3L) Return(1L) Else Return(Fibonacci(n - : missing value where TRUE/FALSE required Calls: print -> Fibonacci Execution interrupted

Could someone help me?

Answer 1

The function readline does not work well in non-interactive use. From the function documentation itself we read:

In non-interactive use the result is as if the Response was RETURN and the value is "".

That is, in non-interactive use, it is as if you have passed the value "" which is an empty string. Next you do as.integer("") which results in NA - so the comparison gives problem.

In non-interactive use (calling from the console) you can use the function readLines, as follows:

n <- readLines("stdin",n=1)

The complete script would look like this:

fibonacci <- function (n)
{
  if (n == 1L)
    return (0L)
  else if (n == 2L || n == 3L)
    return (1L)
  else
    return (fibonacci(n - 1L) + fibonacci(n - 2L))
} 

cat("Insira um valor inteiro: \n")
n <- readLines("stdin",n=1)
n <- as.integer(n)

print(fibonacci(n))