Question

I would like to write an if statement that would continue to repeat a question until a certain condition is met

Something like this:

fun<-function(){
  x<-readline("what is x? ")
  if(x>5)
    {print("X must be less than 5")
    **repeat lines 3 & 4**
}else{
  print("Correct")}

}

Sorry for the **- but I’m not really sure how to correctly write that line. What I am looking to do is to have the prompt “what is x” repeated every time a number greater than 5 is inputted until a number less than five is given. In theory the function would look like this

fun()
what is x? 6
X must be less than 5
what is x? 8
X must be less than 5
what is x? 3
Correct

Answer 1

readline returns a character vector, so you need to coerce it to numeric before the if. Then you can use a while loop (as others have pointed out).

fun <- function() {
  x <- as.numeric(readline("what is x? "))
  if(is.na(x)) stop("x must be a number")
  while(x > 5) {
    print("X must be less than 5")
    x <- as.numeric(readline("what is x? "))
    if(is.na(x)) stop("x must be a number")
  }
  print("Correct")
}