I'm trying to figure out how to incorporate 3 variables into my tail recursion code for racket

Question

Write a tail recursive function called popadd that models a population with P people at time t = 0 and adds d people per year.

(define (popadd t  P)
  (if (= t 0         


        

Answer 1

You can simply pass along another parameter to the recursion:

(define (popadd t P d)
  (if (= t 0)
      P
      (+ d (popadd (- t 1) P d))))

Or you can define the value, to avoid passing it around - assuming it doesn't need to change:

(define d 100)

(define (popadd t P)
  (if (= t 0)
      P
      (+ d (popadd (- t 1) P))))

Notice that you could do the same with P, if it's ok. It really depends on what's the expected contract for the procedure.