Java中的计算器：如何返回主菜单？答案

【问题标题】：Calculator in Java: How to return to the main menu?Java中的计算器：如何返回主菜单？
【发布时间】：2016-05-26 13:38:23
【问题描述】：

我用 Java 编写了一个计算器程序，在用户完成工作后，我希望发生这种情况：我会问他是否想做更多的操作，如果是，程序应该返回选择输入。如果不是，则中断程序。我应该在代码中添加哪些行？这是我的计算程序：

import java.util.*;
class calc
{
    public static void main(String ar[])
    {
        char choice;
        Scanner in = new Scanner(System.in);
        System.out.println("WELCOME TO SHREYDAN'S CALC 1.0");
        System.out.println(" ");
        System.out.println("YOU CAN DO THE FOLLOWING:");
        System.out.println("+: ADDITION");
        System.out.println("-: SUBTRACTION");
        System.out.println("*: PRODUCT");
        System.out.println("/: QUOTIENT");
        System.out.println("#: SQUARE ROOT");
        System.out.println("^: POWER");
        System.out.println("$: ROUND OFF");
        System.out.println("!: FACTORIAL");
        System.out.println(" ");
        System.out.println("ENTER CHOICE");
        choice=in.next().charAt(0);
        switch(choice)
        {
            case '+':
                System.out.println("ENTER 2 NUMBERS, USER");
                double a=in.nextDouble();
                double b=in.nextDouble();
                System.out.println("SUM = "+(a+b));
                break;
            case '-':
                System.out.println("ENTER 2 NUMBERS, USER");
                double c=in.nextDouble();
                double d=in.nextDouble();
                System.out.println("SUBTRACTING "+d+" FROM "+c+" ... DIFFERENCE = "+(c-d));
                break;
            case '*':
                System.out.println("ENTER 2 NUMBERS, USER");
                double e=in.nextDouble();
                double f=in.nextDouble();
                System.out.println("PRODUCT = "+(e*f));
                break;
            case '/':
                System.out.println("ENTER 2 NUMBERS, USER");
                double g=in.nextDouble();
                double h=in.nextDouble();
                System.out.println("DIVIDING "+g+" BY "+h+" = "+(g/h));
                break;
            case '#':
                System.out.println("ENTER NO. FOR SQAURE ROOT:");
                double sqrt=in.nextDouble();
                System.out.println("SQUARE ROOT OF "+sqrt+" = "+Math.sqrt(sqrt));
                break;
            case '^':
                System.out.println("ENTER BASE, USER");
                double base=in.nextDouble();
                System.out.println("ENTER POWER, USER");
                double power=in.nextDouble();
                System.out.println(base+" RAISED TO POWER "+power+" = "+Math.pow(base,power));
                break;
            case '$':
                System.out.println("ENTER DECIMAL VALUES TO ROUND OFF");
                double deci=in.nextDouble();
                System.out.println("THE NEAREST ROUND OFF = "+Math.round(deci));
                break;
            case '!':
                System.out.println("ENTER A NO. FOR FACTORIAL:");
                int fact=in.nextInt();
                int factorial=1;
                for(int i=fact; i>=1;i--)
                    factorial=factorial*i;
                System.out.println(fact+"! = "+factorial);
                break;
            default:
                System.out.println("WRONG CHOICE USER");
        }
    }
}

【问题讨论】：

标签： java menu switch-statement

【解决方案1】：

while 循环是解决此类问题的最佳选择，只需考虑一个用户可以选择切换布尔条件的条件。

例如，如果用户在“继续操作”选项中选择否，则将布尔值切换为 false 并退出 while 循环以结束程序。

【讨论】：

【解决方案2】：

您需要将程序逻辑包装在一个循环中。尝试使用 while 循环

public static void main(String args[])
{
    boolean doContinue = true;
    while(doContinue){
        char choice;
        Scanner in = new Scanner(System.in);
        //program logic
        //when the user enters a command to end
        // set continue=false

    }
}

【讨论】：

恐怕continue 是保留关键字，这段代码无法编译。顺便说一句，你甚至不需要这个变量，你可以使用break 退出循环。
伪代码实际上没有保留字。不过，在这个主题上，他们使用 switch 语句，使用“break”关键字退出循环会使事情变得更加混乱（阅读）。
您应该编写伪代码或 Java 代码。如果你写的是前者，不要使用public static void main(String args[])之类的东西，一般要明确表示是伪代码。关于break 的好点，但是您可以使用标签。
while(true) 更难弄清楚发生了什么。 while(someCondition) 给了我一些东西来查看代码。我可以找到 someCondition 发生变化的所有地方，找到“break”会更难。

【解决方案3】：

也许将整个程序放在一个 while 循环中，并带有一个继续运行 bool 条件，当他们想退出时可以将其设置为 false

【讨论】：

【解决方案4】：

您可以尝试以下方法：

import java.util.*;

class calc {
    public static void main(String ar[]) {
        char choice;
        Scanner in = new Scanner(System.in);
        System.out.println("WELCOME TO SHREYDAN'S CALC 1.0");
        System.out.println(" ");

        boolean loop = true;
        while (loop) {
            System.out.println("YOU CAN DO THE FOLLOWING:");
            System.out.println("+: ADDITION");
            System.out.println("-: SUBTRACTION");
            System.out.println("*: PRODUCT");
            System.out.println("/: QUOTIENT");
            System.out.println("#: SQUARE ROOT");
            System.out.println("^: POWER");
            System.out.println("$: ROUND OFF");
            System.out.println("!: FACTORIAL");
            System.out.println(" ");
            System.out.println("ENTER CHOICE");
            choice = in.next().charAt(0);
            switch (choice) {
                case '+':
                    System.out.println("ENTER 2 NUMBERS, USER");
                    double a = in.nextDouble();
                    double b = in.nextDouble();
                    System.out.println("SUM = " + (a + b));
                    break;
                case '-':
                    System.out.println("ENTER 2 NUMBERS, USER");
                    double c = in.nextDouble();
                    double d = in.nextDouble();
                    System.out.println("SUBTRACTING " + d + " FROM " + c + " ... DIFFERENCE = " + (c - d));
                    break;
                case '*':
                    System.out.println("ENTER 2 NUMBERS, USER");
                    double e = in.nextDouble();
                    double f = in.nextDouble();
                    System.out.println("PRODUCT = " + (e * f));
                    break;
                case '/':
                    System.out.println("ENTER 2 NUMBERS, USER");
                    double g = in.nextDouble();
                    double h = in.nextDouble();
                    System.out.println("DIVIDING " + g + " BY " + h + " = " + (g / h));
                    break;
                case '#':
                    System.out.println("ENTER NO. FOR SQAURE ROOT:");
                    double sqrt = in.nextDouble();
                    System.out.println("SQUARE ROOT OF " + sqrt + " = " + Math.sqrt(sqrt));
                    break;
                case '^':
                    System.out.println("ENTER BASE, USER");
                    double base = in.nextDouble();
                    System.out.println("ENTER POWER, USER");
                    double power = in.nextDouble();
                    System.out.println(base + " RAISED TO POWER " + power + " = " + Math.pow(base, power));
                    break;
                case '$':
                    System.out.println("ENTER DECIMAL VALUES TO ROUND OFF");
                    double deci = in.nextDouble();
                    System.out.println("THE NEAREST ROUND OFF = " + Math.round(deci));
                    break;
                case '!':
                    System.out.println("ENTER A NO. FOR FACTORIAL:");
                    int fact = in.nextInt();
                    int factorial = 1;
                    for (int i = fact; i >= 1; i--)
                        factorial = factorial * i;
                    System.out.println(fact + "! = " + factorial);
                    break;
                default:
                    System.out.println("WRONG CHOICE USER");
            }
            System.out.println("Want to calculate more?Y/N");
            loop = in.next().charAt(0) == 'Y';
        }
    }
}

【讨论】：