How to parse a string in a calculator in R? - r

Question

I wrote a calculator program in which the User enters two numbers and an arithmetic operation between the numbers, then presses Enter and gets the result, or rather did a string parsing, but it doesn't work. What can this be related to? I also wrote the code so that I could exit the function
add<- function(x,y){
return(x+y)
}
subtract <- function(x,y){
return(x-y)
}
multiply <- function(x, y) {
return(x * y)
}
div <- function(x,y){
if(y==0){
return("Error")
break
}
else if(y!=0){
return(x%/%y)
}
}
res<-NA
repeat{
print("9", quote=FALSE)
user_string <-
readline(prompt = ("Enter: "))
if(user_string== 9){
break # to stop the programme
}
components_of_user_string <-
unlist(strsplit(user_string, split = '')) #splitting the line
num1<-as.numeric(components_of_user_string[1]) #first number
num2<-as.numeric(components_of_user_string[3]) # second number
us_chosen_operation <-
components_of_user_string[2]
operations_vector <-
c('+', '-', '*', '/')
choice <- match(us_chosen_operation, operations_vector)
operator <- switch(choice, ' + ', ' - ', ' * ', ' / ')
result <-
switch(
choice,
add(num1, num2),
subtract(num1, num2),
multiply(num1, num2),
divide(num1, num2)
)
print(paste(num1, operator, num2, "=", result))
}

Answer 1

String parsing with eval(parse(...)) could be an option :
repeat {
input <- readline(prompt = ("Enter: "))
print(eval(parse(text = input)))
}
# Enter: (-4)+2
# [1] -2
# Enter: raise_to_degree(2,3)
# [1] 8