# Arrays for items and quantities
items <- character(0)
quantities <- numeric(0)

# Function to add item
add_item <- function(item, quantity) {
  items <<- c(items, item)
  quantities <<- c(quantities, quantity)
  cat("Item added.\n")
}

# Function to update quantity
update_quantity <- function(item, quantity) {
  if (item %in% items) {
    quantities[which(items == item)] <<- quantity
    cat("Quantity updated.\n")
  } else cat("Item not found.\n")
}

# Function to display inventory
display_inventory <- function() {
  for (i in 1:length(items)) {
    cat(items[i], ":", quantities[i], "\n")
  }
}

# Main program loop
repeat {
  choice <- as.integer(readline("1. Add 2. Update 3. Display 4. Exit: "))
  if (choice == 1) {
    item <- readline("Item: ")
    quantity <- as.integer(readline("Quantity: "))
    add_item(item, quantity)
  } else if (choice == 2) {
    item <- readline("Item: ")
    quantity <- as.integer(readline("New Quantity: "))
    update_quantity(item, quantity)
  } else if (choice == 3) display_inventory()
  else if (choice == 4) break
  else cat("Invalid option.\n")
}