Question

(define-struct student (first last major age))

(define student1 (make-student "David" "Smith" 'Math 19))
(define student2 (make-student"Joe" "Jones" 'Math 21))
(define student3 (make-student "Eli" "Black" 'Spanish 20))

(define (same-age? s1 s2)
  (string=? (student-age s1)
            (student-age s2)))

so I am trying to get a boolean as an output if two students are the same age, but when I run it, it says it expects a string as the 1st argument, but given 19. What is the problem?

Answer 1

You create students with their age fields being integers, not strings (note the lack of double-quotation marks), then try to use string=? function to compare them. You should either use the = function to compare on age:

(define-struct student (first last major age))

(define student1 (make-student "David" "Smith" 'Math 19))
(define student2 (make-student "Joe" "Jones" 'Math 21))
(define student3 (make-student "Eli" "Black" 'Spanish 20))

(define (same-age? s1 s2)
  (= (student-age s1)
     (student-age s2)))

or create students with their age fields represented as strings:

(define-struct student (first last major age))

(define student1 (make-student "David" "Smith" 'Math "19"))
(define student2 (make-student "Joe" "Jones" 'Math "21"))
(define student3 (make-student "Eli" "Black" 'Spanish "20"))

(define (same-age? s1 s2)
  (string=? (student-age s1)
            (student-age s2)))