循环为什么下面的代码不能正常工作？（爪哇）

1 年，11 月 Questions & Answers 87

我的目标是接收用户输入，并找出它是否是质数

“我花了好几个小时在这件事上，它几乎奏效了。然而，当我输入2或3时，我什么也得不到。do-while循环只是跳到下一个迭代

我创建的for循环不适用于2或3，因此我为此创建了一个单独的if语句。问题是，它不起作用。我不知道为什么，只知道它可能不会执行

import java.util.Scanner;

public class Lab4a {
    public static void main (String [] args) {
    Scanner scnr = new Scanner(System.in); //creates a Scanner that will receive user input
    boolean isPrime = false; //this, in the end, is where the "primeness" of the input is stored
    int num; //the variable which will store the user input
    boolean isOver = false; //is true once the "primeness" of the input has been decided

    do { //executes at least once
        System.out.println("Enter a positive integer or 0 to exit:"); //prompts the user for input
        num = scnr.nextInt(); //stores the input

        if (num == 0) { //if the number is zero, the loop terminates; if it's negative, the loop terminates as well
            System.exit(0);
        } else if (num < 0) {
            System.out.println("Please enter a positive integer.");
            System.exit(1);
        }

        for (int mult = 2; mult <= num/2; mult++) { //divides the user input by 2, tests for if anything remains; increments by one up to the half of the number. If a remain is encountered,
                                                    // isPrime becomes false and isOver true and the for loop is terminated. If not, the for loop will end with isPrime true and isOver false
            if (num % mult == 0) {
                isPrime = false;
                isOver = true;
                break;
            } else {
                isPrime = true;
                isOver = true;
            }

        }

        if (num == 2 || num == 3) { //the for test above does not work if the user input is 2 or 3, so a separate if statement tests for that
            isPrime = true;
        }
    } while (!isOver); //if isOver is true, the while loop ends



        if (isPrime == true) { //prints the appropriate answer
            System.out.println(num + " is prime.");
        } else {
            System.out.println(num + " isn't prime.");
        }
    }
}

我通常会自己解决这些问题，但我又一次在这方面花了4个小时的时间，我还有另一个类似的程序要写，还有一个微积分测验要准备明天，在这个测验中我对杰克·拉什一清二楚。我真的很绝望

TL；DR:当我输入2或3时，程序不能正常工作；可能是因为if语句没有运行。除此之外，我一无所知

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循环为什么下面的代码不能正常工作？（爪哇）

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