Java 中的计算器：如何返回主菜单？

Question

I've writter a calculator program in Java, after a user is done with work, I want this to happen: i'll ask if he wants to do more operations, if yes, the program should return to choice input. If no, break the program. What lines should I add to the code? This is my calc program:

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");
        }
    }
}

Answer 1

You need to wrap the program logic in a loop. Try using a while loop

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

    }
}

Answer 2

while loops are your best bet for this type of problem, just think of a condition which the user can choose to toggle the boolean condition.

for example if the user chooses no on the "continuing of operations" choice, then toggle the boolean to false and exit the while loop to end the program.

Answer 3

也许将整个程序放在 while 循环中，并带有 continue to run bool 条件，当他们想退出时可以将其设置为 false

Answer 4

You can try the following:

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';
        }
    }
}