教孩子简单加减法的Java程序

Question

I feel like I'm almost there with the code but the problem is the while loop I am not allowed to use break and continue statements for this program. The first output test its suppose to have 14 questions where you get 12 right and 2 wrong giving you 86%. As for the second test you get a perfect score while the last test takes you to 20 questions that being the max number of questions, 4 of the first 8 questions correctly and 4 of the first 8 incorrectly, and then the next 12 correctly giving you 80% Code below:

package proj3;

    import java.util.Scanner;
    
    public class Project4App {
        
        public static void main(String[] args) {
            Scanner scnr = new Scanner(System.in);
            int correctNum = 0;
            int wrongNum = 0;
            double percent = 0;
            int subNumCorrect = 0;
            int subNumWrong = 0;
            int addNumCorrect = 0;
            int addNumWrong = 0;
            int totalQuestions = 0;
            
            
            while(!(correctNum == 10 && totalQuestions == 10) && !(percent >= 85.0 && totalQuestions >= 10) && (totalQuestions != 20)) {
                Question Quest = new Question();
                
                System.out.println("What is the result?" + "\n" + Quest.toString());
                int userInt = scnr.nextInt();
                
                if((Quest.getOperator() == '+') && (userInt == Quest.determineAnswer())) {
                    addNumCorrect += 1;
                }
                else if(Quest.getOperator() == '+' && (userInt != Quest.determineAnswer())) {
                     addNumWrong += 1;
                }
                
                if((Quest.getOperator() == '-') && (userInt == Quest.determineAnswer())) {
                    subNumCorrect += 1;
                }
                else if((Quest.getOperator() == '-') && (userInt != Quest.determineAnswer())) {
                     subNumWrong += 1;
                }
                   
                if(userInt == Quest.determineAnswer()){
                    correctNum += 1;
                    System.out.println("Congratulations, you got it correct!");
                }
                else if (userInt != Quest.determineAnswer()){
                    wrongNum += 1;
                    System.out.println("The correct answer for " + Quest.toString() + " is " + Quest.determineAnswer());
                }
                
                totalQuestions++;
                
                percent = Math.round((double)(correctNum * 100) / (totalQuestions));
                }
                
                System.out.println("\nProgress Report: " + "\nAddition:\nYou got " + addNumCorrect + " correct and " + addNumWrong + " incorrect.");
                System.out.println("Progress Report: " + "\nSubtraction:\nYou got " + subNumCorrect + " correct and " + subNumWrong + " incorrect.");
                System.out.println("The percent correct: " + percent + "%");
                
                
                scnr.close();
            }
        }

Answer 1

I think this largely does what you want. A number of the counters weren't being modified as was intended. This is partly due to the amount going on in your main method making it hard to see what's going on (too much information). I've extracted functionality to smaller, more well defined methods.

You had a whole lot of logic effectively saying you want the user to have achieved 85% with at least 10 questions answered - and stop when 20 questions are asked. You could factor this condition out to a method returning a boolean isGameComplete(totalQuestions) and put this in the while condition-expression.

I've taken the liberty of implementing a question class based on the functionality that I think achieves the intention.

The correctPercent was rounded to an int which made it impossible to be == to 85.5%, say. I've converted this to a double so if you get more than 85% , say 85.25% , the game completes successfully.

Probably some other stuff I've added, which I've tried to comment in-line, if significant. Hopefully this is what you were after.

If it ever gets too difficult to understand, extracting small chunks of code to well named methods (even long ones) helps enormously, since it reduces your mental load.

class Project4App {

    static final Scanner scanner = new Scanner(System.in);
    static int correctNum = 0;
    static int wrongNum = 0;
    static int subNumCorrect = 0;
    static int subNumWrong = 0;
    static int addNumCorrect = 0;
    static int addNumWrong = 0;
    static int totalQuestions = 0;
    static double percentCorrect = 0;

    public static void main(String[] args) {
        /**
         * answer at least 9/10 questions correctly (to get 85%)
         */
        while (percentCorrect < 85.0 && totalQuestions >= 10 && totalQuestions <= 20) {
            Question question = new Question();

            int userInt = getUsersAnswer(question);
            boolean isCorrect = question.determineAnswer(userInt);
            updateStatistics(question, isCorrect);
            printResults(); // can remove this/comment this out - added to help with debugging
        }

        System.out.println();
        System.out.println("------------ Game Complete! ------------");
        printResults();
    }

    private static void printResults() {
        System.out.println("\nProgress Report: " + "\nAddition:\nYou got " + addNumCorrect + " correct and " + addNumWrong + " incorrect.");
        System.out.println("Progress Report: " + "\nSubtraction:\nYou got " + subNumCorrect + " correct and " + subNumWrong + " incorrect.");
        System.out.println("The percent correct: (" + (addNumCorrect+subNumCorrect) + "/" + totalQuestions +") " + percentCorrect + "%");
        System.out.println("The percent wrong: (" + (addNumWrong+subNumWrong) + "/" + totalQuestions +") " + (100 - percentCorrect) + "%");
    }

    private static int getUsersAnswer(Question question) {
        System.out.println("What is the result?" + "\n" + question.toString());
        int userInt = scanner.nextInt();
        return userInt;
    }

    public static void updateStatistics(Question question, boolean isCorrect){
        if (question.getOperator() == '+') {
            if (isCorrect) {
                addNumCorrect++;
                correctNum++; // newly added (wasn't updated)
            } else {
                addNumWrong++;
                wrongNum++; // newly added - unused variable originall
            }
        } else { // operator is '-'
            if (isCorrect) {
                subNumCorrect++;
                correctNum++; // newly added (wasn't updated)
            } else {
                subNumWrong++;
                wrongNum++; // newly added - unused variable originall
            }
        }
        totalQuestions++; // newly added
        percentCorrect = (correctNum * 100) / totalQuestions;
    }
}

class Question {

    private static final int UPPER_LIMIT_ON_RANDOM_NUMBERS = 20;
    private static final Random random = new Random();
    private final int number1;
    private final int number2;
    private final char operator;

    public Question() {
        operator = Math.random()>0.5 ? '+' : '-';
        number1 = random.nextInt(UPPER_LIMIT_ON_RANDOM_NUMBERS); // NOTE THE SUBTRACTION NUMBER COULD BE NEGATIVE IF number2
        number2 = random.nextInt(UPPER_LIMIT_ON_RANDOM_NUMBERS); // IS GREATER THAN number1.
    }

    public char getOperator() {
        return operator;
    }

    public boolean determineAnswer(int userAnswer) {
        switch (operator) {
            case '+':
                return userAnswer == (number1 + number2);
            case '-':
                return userAnswer == (number1 - number2);
        }
        return false; // shouldn't end up here - would be better to throw an unchecked exception and crash the program - new RuntimeException()
    }

    @Override
    public String toString() {
        return number1 + " " + operator + " " + number2;
    }
}

Output:

------------ Game Complete! ------------

Progress Report: 
Addition:
You got 7 correct and 0 incorrect.
Progress Report: 
Subtraction:
You got 2 correct and 1 incorrect.
The percent correct: (9/10) 90.0%
The percent wrong: (1/10) 10.0%