java - Java程序中的加法等于不同的值

Question

我的 Java 代码有问题。这是一份可以计算您的成绩的问卷。一切都很顺利，直到最后一部分显示“当前分数”，整个方程应该等于 33.16，但实际上却等于 24。

我更改了一些值，做了一些研究，但我还没有找到我要找的东西。

import java.util.Scanner;

public class GradeCalculator {

    public static void main(String[] args) {
        System.out.println("Grading Scale:");
        System.out.println("A\t 90 - 100");
        System.out.println("B\t 80 - 89");
        System.out.println("C\t 70 - 79");
        System.out.println("D\t 60 - 69");
        System.out.println("F\t below 60");

        System.out.println("What letter grade do you want to achieve for the course?");
        String desiredGrade;

        Scanner keyboard = new Scanner(System.in);
        desiredGrade = keyboard.next();

        if (desiredGrade.equalsIgnoreCase("A") || desiredGrade.equalsIgnoreCase("B")
                || desiredGrade.equalsIgnoreCase("C") || desiredGrade.equalsIgnoreCase("D")
                || desiredGrade.equalsIgnoreCase("F")) {// is this necessary? vv
            System.out.println("Enter Percentage Weights");
        }

        else {
            System.out.println("Input error.");
            System.exit(0);
        }

        int exam1, exam2, finalExam, labs, projects, attendance, quizzes;

        System.out.println("Exam 1:\t");
        exam1 = keyboard.nextInt();

        System.out.println("Exam 2:\t");
        exam2 = keyboard.nextInt();

        System.out.println("Final Exam:\t");
        finalExam = keyboard.nextInt();

        System.out.println("Labs:\t");
        labs = keyboard.nextInt();

        System.out.println("Projects:\t");
        projects = keyboard.nextInt();

        System.out.println("Attendance:\t");
        attendance = keyboard.nextInt();

        System.out.println("Quizzes:\t");
        quizzes = keyboard.nextInt();

        // so the semicolon isn't needed after the if statement?
        if (exam1 + exam2 + finalExam + labs + projects + attendance + quizzes != 100) {
            System.out.println("Weights don't add up to 100, program exiting");
            System.exit(0);
        }

        System.out.println("Enter your scores out of a 100:");
        System.out.println("Do you know your Exam 1 score?");

        String answer;
        int exam1score = 0, exam2score = 0, finalExamScore = 0, labAverage = 0, projectAverage = 0, quizAverage = 0, attendanceAverage = 0;
        double currentScore = 0;
        answer = keyboard.next();

        // ask about this

        if (answer.equalsIgnoreCase("yes") || answer.equalsIgnoreCase("y")) {
            // why can't i put int here?
            System.out.println("Score received on exam 1:");
            exam1score = keyboard.nextInt();

            System.out.println("Do you know your Exam 2 score?");
            answer = keyboard.next();

            if (answer.equalsIgnoreCase("yes") || answer.equalsIgnoreCase("y")) {
                System.out.println("Score received on exam 2:");
                exam2score = keyboard.nextInt();

                System.out.println("Do you know your Final Exam score?");
                answer = keyboard.next();
           }
           if (answer.equalsIgnoreCase("yes") || answer.equalsIgnoreCase("y")) {
                System.out.println("Score received on final exam");
                finalExamScore = keyboard.nextInt();
            }
        }

        System.out.println("Do you know your lab average?");
        answer = keyboard.next();
        if (answer.equalsIgnoreCase("yes") || answer.equalsIgnoreCase("y")) {
                System.out.println("Average Lab Grade:");
                labAverage = keyboard.nextInt();
        }

        System.out.println("Do you know your project average?");
        answer = keyboard.next();
        if (answer.equalsIgnoreCase("yes") || answer.equalsIgnoreCase("y")) {
            System.out.println("Average Project Grade:");
            projectAverage = keyboard.nextInt();
        }

        System.out.println("Do you know your quiz average?");
        answer = keyboard.next();
        if (answer.equalsIgnoreCase("yes") || answer.equalsIgnoreCase("y")) {
            System.out.println("Average Quiz Grade:");
            quizAverage = keyboard.nextInt();
        }

        System.out.println("Do you know your attendance average?");
        answer = keyboard.next();
        if (answer.equalsIgnoreCase("yes") || answer.equalsIgnoreCase("y")) {
            System.out.println("Average Attendance Grade:");
            attendanceAverage = keyboard.nextInt();
        }

        currentScore = ((double)exam1score*exam1 + exam2score*exam2 +finalExam*finalExamScore + labs*labAverage + projects*projectAverage + attendance*attendanceAverage + quizzes*quizAverage)/((double)exam1+exam2+finalExam+labs+projects+attendance+quizzes);
        System.out.println("Current Grade Score:\t " + currentScore);

        String grade;

        if (currentScore >= 90)
            grade = "A";
        else if (currentScore >= 80)
            grade = "B";
        else if (currentScore >= 70)
            grade = "C";
        else if (currentScore >= 60)
            grade = "D";
        else
            grade = "F";
    }
}

Answer 1

以下仅将 exam1score*exam1 值转换为 double，而不是整个表达式。

(double) exam1score*exam1 + exam2score*exam2 + finalExam*finalExamScore + ....

所以，你应该这样做。

int nominator = exam1score*exam1 + exam2score*exam2 + finalExam*finalExamScore 
                        + labs*labAverage + projects*projectAverage 
                        + attendance*attendanceAverage + quizzes*quizAverage;
int denominator = exam1 + exam2 + finalExam + labs + projects + attendance + quizzes;
currentScore = (double) nominator / denominator;

或者

int nominator = exam1score*exam1 + exam2score*exam2 + finalExam*finalExamScore
                        + labs*labAverage + projects*projectAverage 
                        + attendance*attendanceAverage + quizzes*quizAverage);
int denominator = exam1 + exam2 + finalExam + labs + projects + attendance + quizzes;
currentScore = (nominator * 1.0) / denominator;