使用if语句java添加while循环

Question

我正在为学校做一个简单的Java计算器，效果很好。但是，我需要添加一个while循环，询问用户是否要继续是/否。不过，我不知道应该将while语句放在哪里。我试着把if语句放在上面，我试着把它放在下面，然后把它添加到每个if和else if语句中，但仍然无法让它工作。在if和else-if语句中，应该在哪里放置while循环，以获得运行while循环的所有选项？

while (input.toUpperCase().equals("y"))
System.out.println("Do you want to continue? (y/n)");
input = calc.nextLine();

import java.util.Scanner;

public class loops { 

public static void main(String[] args) {

Scanner calc = new Scanner (System.in);
double firstNum, secondNum, answer;
String input = "";

System.out.println("what would you like to do");
System.out.println("a. Add two numbers. ");
System.out.println("b. Subtract two numbers. ");
System.out.println("c. Multiply two numbers. ");
System.out.println("d. Divide two numbers. ");
System.out.println("Select a letter");
input.calc.nextLine();

if (input.equals("a")) {

System.out.println("Please enter your first number: ");
firstNum = calc.nextDouble();
System.out.println("Enter your second number: ");
secondNum = calc.nextDouble();

answer = firstNum + secondNum;
System.out.println("your answer is: " + String.valueOf (answer));

else if (input.equals("b")) {
System.out.println("Please enter your first number: ");
firstNum = calc.nextDouble();
System.out.println("Enter your second number: ");
secondNum = calc.nextDouble();

answer = firstNum - secondNum;
System.out.println("your answer is: " + String.valueOf (answer));
}

}
}
}

Answer 1

您可以使用do-time循环来实现您的功能。do-time将至少执行一次，然后检查连续运行表达式的真假。

您的代码有2个职责：

1. calculate the sum of 2 numeric inputs.
2. checks continuous calculating or not.

其中一个解决方案是将这两个功能分离，并使添加/删除其中任何一个功能变得更容易。测试/调试代码很容易。

import java.util.*;

public class Test{
    static Scanner calc = new Scanner(System.in);
    static String input ="";
    static boolean keepRunning = false;
    double firstNum, secondNum, answer;


    public static void main(String[]args){
        Test test = new Test();
        do{
            test.calculate(calc);  // calculate your 2 numeric inputs

            // update boolean flag indicate continuous calculating or stop
            System.out.print("Do you want to continue? (y/n)");
            input = calc.next();
            keepRunning = input.toLowerCase().equals("y");
        }while(keepRunning);

    }

    public void calculate(Scanner calc){
        System.out.print("Please ,enter your first number:  ");
        firstNum = calc.nextDouble();
        System.out.print("Enter your second number: ");
        secondNum = calc.nextDouble();

        answer = firstNum + secondNum;
        System.out.println("Your answer is: " + String.valueOf(answer));
    }
}

Answer 2

正如前面指出的，应该使用do while循环，但是如果您想使用while循环，那么您的代码应该如下所示-

Scanner calc = new Scanner(System.in);
double firstNum, secondNum, answer;
String input ="y";



  while (input.toUpperCase().equals("y")) {
        System.out.print("Do you want to continue? (y/n)");
        input = calc.nextLine();
        if (input.equals("a")) {
             System.out.print("Please ,enter your first number:  ");
             firstNum = calc.nextDouble();
             System.out.print("Enter your second number: ");
             secondNum = calc.nextDouble();

             answer = firstNum + secondNum;
             System.out.println("Your answer is: " + String.valueOf(answer));    
             }
    }

Answer 3

我认为在这种情况下，您应该在while中放入if-else。看起来您希望在特定情况下执行if，因此正确的方法是使用某种条件循环围绕if（如果您希望它至少运行一次，这里也可以使用do）。

编辑：您还需要在时修复上的条件。如问题评论中所述，输入。toUpperCase（）。等于（“y”）的计算结果永远不会为true。