Simple Calculator in R
# Program make a simple calculator
# that can add, subtract, multiply
# and divide using functions

add <- function(x, y) {
    return(x + y)
}

subtract <- function(x, y) {
    return(x - y)
}

multiply <- function(x, y) {
    return(x * y)
}

divide <- function(x, y) {
    return(x / y)
}

# take input from the user
print("Select operation.")
print("1.Add")
print("2.Subtract")
print("3.Multiply")
print("4.Divide")

choice = as.integer(readline(prompt="Enter choice[1/2/3/4]: "))

num1 = as.integer(readline(prompt="Enter first number: "))
num2 = as.integer(readline(prompt="Enter second number: "))

operator <- switch(choice,"+","-","*","/")
result <- switch(choice, add(num1, num2), subtract(num1, num2), multiply(num1, num2), divide(num1, num2))

print(paste(num1, operator, num2, "=", result))
Output

[1] "Select operation."
[1] "1.Add"
[1] "2.Subtract"
[1] "3.Multiply"
[1] "4.Divide"
Enter choice[1/2/3/4]: 4
Enter first number: 20
Enter second number: 4
[1] "20 / 4 = 5"