Student Grade Calculator in LISP

The program performs the following key functions:

1. Takes user input for the three scores, each between 0 and 100.
2. Validates that the entered scores are numbers within the correct range.
3. Calculates the average of the three scores.
4. Determines the letter grade (A–F) based on the calculated average:

A: 90–100

B: 80–89

C: 70–79

D: 60–69

F: below 60

Displays the results: individual scores, average score (formatted to 2 decimal places), and final letter grade.

Program:-

;; Student Grade Calculator

(defun calculate-grade (total)

(cond ((>= total 90) "A")

((>= total 80) "B")

((>= total 70) "C")

((>= total 60) "D")

(t "F")))

(defun get-valid-score (prompt min max)

(format t "~%~A (Enter score between ~D and ~D): " prompt min max)

(let ((score (read)))

(if (and (numberp score) (>= score min) (<= score max))

score

(progn

(format t "Invalid score! Please enter a number between ~D and ~D~%" min max)

(get-valid-score prompt min max)))))

(defun main ()

(format t "~%Welcome to Student Grade Calculator~%")

;; Get scores for different components

(let* ((assignment (get-valid-score "Enter Assignment score" 0 100))

(midterm (get-valid-score "Enter Midterm score" 0 100))

(final (get-valid-score "Enter Final exam score" 0 100))

;; Calculate weighted total

(total (/ (+ assignment midterm final) 3))

(final-grade (calculate-grade total)))

;; Display results

(format t "~%Results:~%")

(format t "Assignment Score: ~D~%" assignment)

(format t "Midterm Score: ~D~%" midterm)

(format t "Final Score: ~D~%" final)

(format t "Average Score: ~,2F~%" total)

(format t "Final Grade: ~A~%" final-grade)))

;; Run the program

(main)

Output: