Question

我正在创建一个子菜单，允许用户增加库存，减少库存并退出子菜单。我在为子菜单创建循环时遇到了一些问题。我正在使用do-while循环，但它并没有像我预期的那样工作。我使用布尔来控制循环，以及switch和case语句。我必须忽略代码中的一个小细节：

import java.util.*; //Scanner

public class tester2
{
    public static void main (String []args)
    {
        int bookStock = 100; // Sets current bookStock amount to 100
        boolean subMenuControl = false; // controls the loop for sub menu 
        do
        {
            System.out.println("\nMake your seletion from the choices below:\n"); //Prints this on screen to instruct user

            System.out.println("A. Increase Stock Availability"); 
            System.out.println("B. Reduce Stock Availability");
            System.out.println("C. Quit\n"); 

            System.out.print("Your choice? "); //Prompts user for a choice only A,B,C or a,b,c are valid
            Scanner subMenuInput = new Scanner(System.in); //reads user choice from keyboard eg. A,B,C or a,b,c
            String subMenuChoice  = subMenuInput.nextLine(); //stores users selection into variable subMenuChoice 
            char subMenuAccess = subMenuChoice.charAt(0); //manipulates String into char

                switch (subMenuAccess) //reads user input from variable and performs switch statement
                {
                    case 'A': //Doesnt matter if user enters in lower or upper case
                    case 'a':
                        System.out.print("\nHow many books do you wish to add to stock: "); //prints to screen 
                        Scanner increaseInput = new Scanner(System.in); //reads userinput 
                        int increaseStockAmount = increaseInput.nextInt(); //stores userinut as interger 

                        bookStock += increaseStockAmount; //increases bookStock by input amount
                        System.out.println("\nCurrent Stock is now: " + bookStock); // displays new bookstock amount
                    break; //exits case statement
                    case 'B': //Doesnt matter if user enters in lower or upper case
                    case 'b':
                        System.out.print("\nHow many books do you wish to reduce from stock: ");  //prints to screen
                        Scanner reduceInput = new Scanner(System.in); //reads userinput
                        int reduceStockAmount = reduceInput.nextInt(); //stores userinut as interger

                            if (bookStock >= reduceStockAmount) //checks if user can reduce stock amount 
                            {
                                bookStock -= reduceStockAmount; //reduces bookStock by input amount
                                System.out.println("\nCurrent Stock is now: " + bookStock); //displays new bookstock amount
                            }
                            else
                            {
                                System.out.println("\nCurrent Stock is " + bookStock + " can not reduce stock by " + reduceStockAmount); //displays to user that they can not reduce stock by entered amount
                            }
                    break; //exits case statement
                    case 'C': //Doesnt matter if user enters in lower or upper case 
                    case 'c':
                        System.out.print("\nQuitting... ");
                        subMenuControl = true; //exits subMenu
                    break; //exits case statement
                }
        }
        while (subMenuControl = false);
    }
}

此程序的以下输出不会循环任何内容。任何建议都会非常有帮助。谢谢

我试过了（subMenuControl == false）;在提出这个问题之前，它会返回错误。

程序运行但在提示用户输入后，它退出并且不再显示子菜单。我不希望它，除非...将添加subMenuControl = false;在每种情况下声明使它工作？

输出以下内容：

从以下选项中进行选择：

一个。增加库存可用性 B.减少库存可用性 C.退出

你的选择？一个

您希望将多少本书添加到库存中：7

现有股票现在：107

然后退出。

Answer 1

您的问题是，您要将值false分配给subMenuControl

while (subMenuControl = false);

这将始终评估为false。

如果您想要做的是重复while循环，只要subMenuControl为false，您就会想要写

while (!subMenuControl);

!是NOT运算符，因此它前面的任何布尔值都将计算为相反的值。在这种情况下，循环将重复，subMenuControl为假，如果为真则结束。

do-while循环使用boolean，switch和case语句

1 个答案: