Notes

;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-beginner-reader.ss" "lang")((modname sparplan-template) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ())))
;; Authors: GLOWKA HAQUE

;; Error tolerance: 3 decimal digits
(define tolerance 0.001)

;; === Problem 9.1 ===

;; add-interest: number number--> number
;; nimmt Kapital und Zinssatz, berechnet daraus das Endkapital
;; Bsp. (add-interest 100 0.01) sollte 101 ausgeben
;;
(define (add-interest capital interest)
(if (> 0 capital) capital


(if(> 0 interest)
(error "add-interest: no negative interest rates allowed")
(+(* capital interest)capital)))
)

;; Tests - these do NOT count as "your" tests!
(check-expect (add-interest 100 0.02) 102)
(check-within (add-interest 1337.15 0.008) 1347.8472 tolerance)
(check-error (add-interest 4711 -0.005) "add-interest: no negative interest rates allowed")

;; === Problem 9.2 ===

;; average-yearly-return:
;;konsumiert Anfangskapital, Endkapital, Vertragslaufzeit und berechnet daraus den Durchschnittszinssatz
;;
(define (average-yearly-return capital-after capital-before years)
(- (expt(/ capital-after capital-before)(/ 1 years))1))

;; Tests - these do NOT count as "your" tests!
(check-within (average-yearly-return 110 100 5) 0.0192 tolerance)
(check-within (average-yearly-return 3500 3000 10) 0.0155 tolerance)

;; === Problem 9.3 ===

;; savings-plan-a: number number --> number
;; konsumiert jeweils das Anfangskapital und die Vertragslaufzeit und geben das Endkapital zurück
;; im falle einer Laufzeitangabe von weniger als einem oder mehr als drei Jahren gibt es einen FEHLER
;;


(define (savings-plan-a capital years)
(cond
[(and(>= years 1)(< years 2))(add-interest capital 0.005) ]
[(and(>= years 2)(< years 3))(add-interest(add-interest capital 0.005) 0.01)]
[(and(>= years 3)(< years 4))(add-interest (add-interest(add-interest capital 0.005) 0.01) 0.015)]
[else (error "savings-plan-a: invalid runtime")]))


;; Tests - these do NOT count as "your" tests!
(check-within (savings-plan-a 1000 1) 1005 tolerance)
(check-within (savings-plan-a 1000 2) 1015.05 tolerance)
(check-within (savings-plan-a 1000 3) 1030.276 tolerance)
(check-error (savings-plan-a 1000 0.5)"savings-plan-a: invalid runtime")
(check-error (savings-plan-a 1000 4) "savings-plan-a: invalid runtime")

;; savings-plan-b:
;;
;;
;;
(define (savings-plan-b capital years)
(cond
[(and(>= years 1)(< years 2))(add-interest capital 0.005) ]
[(and(>= years 2)(< years 3)) (add-interest(add-interest capital 0.005) 0.005)]
[(and(>= years 3)(< years 4))(+ 30(add-interest (add-interest(add-interest capital 0.005) 0.005) 0.005))]
[else (error "savings-plan-b: invalid runtime")]))



;; Tests - these do NOT count as "your" tests!
(check-within (savings-plan-b 1000 1) 1005 tolerance)
(check-within (savings-plan-b 1000 2) 1010.025 tolerance)
(check-within (savings-plan-b 1000 3) 1045.075 tolerance)
(check-error (savings-plan-b 1000 0.5) "savings-plan-b: invalid runtime")
(check-error (savings-plan-b 1000 4) "savings-plan-b: invalid runtime")

;; === Problem 9.4 ====

;; best-savings-plan: number number --> symbol
;;konsumiert Anfangskapital und die Laufzeit, anhand dessen vergleicht er die Sparpläne und gibt den am meisten geeigneten aus
;;
;;
(define (best-savings-plan capital years)
(if (<(savings-plan-b capital years)(savings-plan-a capital years))
'SavingsPlanA
'SavingsPlanB))

;; Tests - these do NOT count as "your" tests!
(check-expect (best-savings-plan 2000 3) 'SavingsPlanA)
(check-expect (best-savings-plan 1000 3) 'SavingsPlanB)
(check-expect (best-savings-plan 500 2) 'SavingsPlanA)