Convert character "pi" to value pi

Question

I am working on a homework that requires two input variables and calculate the value.

input.c.x <-as.numeric(readline("input a variable x: "))
input.c.a<- as.numeric(readline("input a variable a: "))
output <- sin((input.c.a)*(input.c.x))

for variable a, I need to input something like "pi/180". But it will not work as a will be character and it will not converted to numbers like 3.14

Answer 1

Since readline returns output of type "character". We can use eval/parse to convert data

input.c.x <- readline("input a variable x: ")
input.c.a <- readline("input a variable a: ")
x <- eval(parse(text = input.c.x))
y <- eval(parse(text = input.c.a))

and then these numbers can be used for further calculation.

input.c.x <- readline("input a variable x: ")
#input a variable x: pi/180

x <- eval(parse(text = input.c.x))
x
#[1] 0.01745329