Java不返回乘法双精度

我需要计算用户答对的问题的百分比。双右是用户正确回答的许多问题。由于某些原因，当用户正确回答问题时，它不会将更新后的right值返回给main方法。我有所有的数学知识，程序运行正常。我从终端得到的唯一回应是“你得到了0%的正确率。”

import java.util.Scanner；
导入java.util.Random；
公共课程{
公共静态void main（字符串[]args）{
System.out.println（“您想问多少问题？”）；
扫描仪sc=新的扫描仪（System.in）；
双数；
num=sc.nextDouble（）；
双重问题；
双重权利；
右=0.0；
问题=0.0；
双重问题；
提问=提问；
而（questionsimport java.util.Scanner;
import java.util.Random;

public class program {
    public static void main(String[] args) {

        System.out.println("How Many Questions Would You Like?");

        Scanner sc = new Scanner(System.in);
        Double num;
        num = sc.nextDouble();


        Double questions;

        Double right;

        right = 0.0;
        questions = 0.0;

        Double questionsasked;
        questionsasked = questions;

        while (questions < num) { // Compares Initial value of questions to num,is how many questions that the
            // user wants.
            // Ask User What Type Of Problem
            System.out.println("What Kind Of Problem Would You Like?");
            // 1 for Addition, 2 for Subtraction, 3 For Multiplication, 4 for Division
            System.out.println("1 for \"+\", 2 for \"-\", 3 for \"*\", 4 for \"/\"");
            // Takes Input Values For Problem Type
            Scanner sd = new Scanner(System.in);
            Double input;
            input = sc.nextDouble();
            // Register What Problem They Would Like
            // Input is what type of problem user wants
            if (input == 1) {
                // Addition Problem, Passes Number Of Questions Right, and other necessary
                // things
                // Adds Value To Number Of Questions Asked, Used To Find Percentage Correct
                questions = questions + 1.0;
                // Calls Method
                add(right, questions, questionsasked);
            } else if (input == 2) {
                // Subtraction Problem, Passes Number Of Questions Right, and other necessary
                // things
                // Adds Value To Number Of Questions Asked, Used To Find Percentage Correct
                questions = questions + 1.0;
                // Calls Method
                subtract(right, questions, questionsasked);

            } else if (input == 3) {
                // Multiply Problem, Passes Number Of Questions Right, and other necessary
                // things
                // Adds Value To Number Of Questions Asked, Used To Find Percentage Correct
                questions = questions + 1.0;
                // Calls Method
                multiply(right, questions, questionsasked);

            } else if (input == 4) {
                // Division Problem, Passes Number Of Questions Right, and other necessary
                // things
                // Adds Value To Number Of Questions Asked, Used To Find Percentage Correct
                questions = questions + 1.0;
                // Calls Method
                divide(right, questions, questionsasked);

            } else {
                // If Answer to what type of problem they want is not 1-4 it will print this.
                System.out.println("Not A Valid Problem.");
            }
        }
        Double calcper;
        calcper = right / questions;
        Double calcperfinal;
        calcperfinal = calcper * 100;
        System.out.println("You Got " + calcperfinal + "% Correct");

        System.out.println("Program Is Done Running!"); // This Is The Very Last Thing That Happens.
    }

    // Addition Method
    public static Double add(Double right, Double questions, Double questionsasked) {

        System.out.println("OK, Let's Add!");

        Random rand = new Random(); // This Declares The Random Number
        Double rnumber = rand.nextInt((int) 100.0) + 0.0; // 100 Is The Max, 0 Is The Min.

        Random rand2 = new Random(); // This Declares The Random Number
        Double rnumber2 = rand2.nextInt((int) 100.0) + 0.0; // 100 Is The Max, 0 Is The Min.

        System.out.println("What Is, " + rnumber + " + " + rnumber2 + "?"); // This Will Ask Question.

        Scanner sc = new Scanner(System.in);
        Double add; // This Is The User Answer
        add = sc.nextDouble(); // This Sets Current Scanner To The User Answer

        int answer = (int) (rnumber + rnumber2); // Creates INT To Determine The Right Answer

        if (add == answer) { // Compares User Answer To The Correct Computer Answer
            System.out.println("Correct!"); // Prints Out Correct
            right = right + 1.0;
            return right;
            // Used If user Got Question Incorrect
        } else {
            System.out.println("No, the correct answer is " + answer); // Prints The Correct Answer.
            return right;
        }
    }

    // Subtraction Method
    public static Double subtract(Double right, Double questions, Double questionsasked) {

        System.out.println("OK, Let's Subtract!");

        Random rand = new Random(); // This Declares The Random Number
        Double rnumber = (double) (rand.nextInt(100) + 0.0); // 100 Is The Max, 0 Is The Min.

        Random rand2 = new Random(); // This Declares The Random Number
        Double rnumber2 = (double) (rand2.nextInt(100) + 0.0); // 100 Is The Max, 0 Is The Min.

        System.out.println("What Is, " + rnumber + " - " + rnumber2 + "?"); // This Will Ask Question.

        Scanner sc = new Scanner(System.in);
        Double sub; // This Is The User Answer
        sub = sc.nextDouble(); // This Sets Current Scanner To The User Answer

        int answer = (int) (rnumber - rnumber2); // Creates INT To Determine The Right Answer

        if (sub == answer) { // Compares User Answer To The Correct Computer Answer
            System.out.println("Correct!"); // Prints Out Correct
            right = right + 1;
            return right;
            // Used If User Gets Question Incorrect
        } else {
            System.out.println("No, the correct answer is " + answer); // Prints The Correct Answer.
            if (questionsasked == 1.0 || questions == 1.0 && right == 0.0) {
                System.out.println("You Got %0 Right.");
            } else {
                return right;
            }
        }
        return questions; // Updates Value Of Questions Asked
    }

    // Multiplication Method
    public static Double multiply(Double right, Double questions, Double questionsasked) {

        System.out.println("OK, Let's Multiply!");

        Random rand = new Random(); // This Declares The Random Number
        Double rnumber = (double) (rand.nextInt(100) + 0); // 100 Is The Max, 0 Is The Min.

        Random rand2 = new Random(); // This Declares The Random Number
        Double rnumber2 = (double) (rand2.nextInt(100) + 0); // 100 Is The Max, 0 Is The Min.

        System.out.println("What Is, " + rnumber + " * " + rnumber2 + "?"); // This Will Ask Question.

        Scanner sc = new Scanner(System.in);
        Double mul; // This Is The User Answer
        mul = sc.nextDouble(); // This Sets Current Scanner To The User Answer

        int answer = (int) (rnumber * rnumber2); // Creates INT To Determine The Right Answer

        if (mul == answer) { // Compares User Answer To The Correct Computer Answer
            System.out.println("Correct!"); // Prints Out Correct
            right = right + 1.0;
            // Used If User Gets Question Incorrect
        } else {
            System.out.println("No, the correct answer is " + answer); // Prints The Correct Answer.
            return right;
        }
        return questions; // Updates Value Of Questions Asked
    }

    // Division Method
    public static Double divide(Double right, Double questions, Double questionsasked) {

        System.out.println("OK, Let's Divide!");

        Random rand = new Random(); // This Declares The Random Number
        Double rnumber = (double) (rand.nextInt(100) + 0.0); // 100 Is The Max, 0 Is The Min.

        Random rand2 = new Random(); // This Declares The Random Number
        Double rnumber2 = (double) rand2.nextInt(100) + 0.0; // 100 Is The Max, 0 Is The Min.

        System.out.println("What Is, " + rnumber + " / " + rnumber2 + "?" + ", Round To The Nearest 100th Place."); // This

        // Will

        // Ask



        Scanner sc = new Scanner(System.in);
        Double div; // This Is The User Answer
        div = sc.nextDouble(); // This Sets Current Scanner To The User

        double answer = (rnumber / rnumber2); // Creates Double To Determine
        double answerrounded = Math.round(answer * 100.0) / 100.0; // Creates

        if (div == answerrounded) { // Compares User Answer To The Correct
            System.out.println("Correct!"); // Prints Out Correct
            right = right + 1.0;
            return right;
            // used If User Gets Question Incorrect
        } else {
            System.out.println("No, the correct answer is " + answerrounded);

        }
        return questions; // Updates Value Of Questions Asked
    }
}

right = add(right, questions, questionsasked);
...
right = subtract(right, questions, questionsasked);
...
right = multiply(right, questions, questionsasked);
...
right = divide(right, questions, questionsasked);

public static Double add(Double right, Double questions, Double questionsasked)

right = add(right, questions, questionsasked);

while (questions < num) // bad practice

Double num;
num = sc.nextDouble();

switch (input)
{
    case 1:
    {
        ...
        break;
    }
    ...
}

questions = questions + 1.0;

++questions;

 right = add(right, questions, questionsasked);