Money adding program in R - r

Question

I want to create a program in R that takes integer user input and then adds it to the previous user input. ex. user input(say one day): 10, then (maybe the next day) user input: 15 --> output 25.Ideally this would accept nearly an infinite amount of input. here is what I have so far:
amount_spent <- function(){
i <-1
while(i<10){
n <- readline(prompt="How much did you spend?: ")
i<-i+1
}
print(c(as.integer(n)))
}
amount_spent()
Problems I have with this code are that it only saves the last input value, and it is difficult to control when User is allowed to input. Is there any way to save user input to a data that can be manipulated through readline()?

Answer 1

# 1.R
fname <- "s.data"
if (file.exists(fname)) {
load(fname)
}
if (!exists("s")) {
s <- 0
}
n <- 0
while (TRUE) {
cat ("Enter a number: ")
n <- scan("stdin", double(), n=1, quiet = TRUE)
if (length(n) != 1) {
print("exiting")
break
}
s <- s + as.numeric(n)
cat("Sum=", s, "\n")
save(list=c("s"), file=fname)
}
You should run the script like this: Rscript 1.R
To exit the loop press Ctrl-D in Unix, or Ctrl-Z in Windows.

Answer 2

An R-ish way to do it would be through closures. Here is an example for interactive use (i.e. within an R session).
balance_setup <- function() {
balance <- 0
change_balance <- function () {
n <- readline(prompt = "How much did you spend?: ")
n <- as.numeric(n)
if (!is.na(n))
balance <<- balance + n
balance
}
print_balance <- function() {
balance
}
list(change_balance = change_balance,
print_balance = print_balance)
}
funs <- balance_setup()
change_balance <- funs$change_balance
print_balance <- funs$print_balance
Calling balance_setup creates a variable balanceand two functions that can access it: one for changing the balance, one for printing it. In R, functions can only return a single value, so I bundle both functions together as a list.
change_balance()
## How much did you spend? 5
## [1] 5
change_balance()
## How much did you spend? 5
## [1] 10
print_balance()
## [1] 10
If you want many inputs, use a loop:
repeat{
change_balance()
}
Break the loop with Ctrl-C, Escape or whatever is used on your platform.