使用while循环重复一组指令 - Java

Question

我得到用户输入做了一些计算，然后反复要求用户重复执行，直到输入一个Sentinel值（在我的情况下为3）。

我使用do-while循环，它并没有给我想要的输出，如下图所示，

import java.util.Scanner; 
public class Test { 

public static void main(String[] args) { 

    Scanner input = new Scanner(System.in); 

    System.out.println("1: Addition"); 
    System.out.println("2: Multiplication"); 
    System.out.println("3: Exit"); 

    System.out.print("Please choose a number: "); 

    int userinput = input.nextInt(); 

    // Generate two random numbers 
    int number1 = (int)(Math.random() * 10); 
    int number2 = (int)(Math.random() * 10); 
    do { 
     if (userinput == 1) { 
      System.out.print("What is " + number1 + " + " + number2); 
      int answer = input.nextInt(); 
      int tureanswer = number1 + number2; 

      if (answer == tureanswer){ 
       System.out.println("You're correct"); 
      } 
      else 
       System.out.println("Wrong,correct answer is " + tureanswer); 
     } 
     if (userinput == 2) { 
      System.out.print("What is " + number1 + " * " + number2 + " : "); 
      int answer = input.nextInt(); 
      int tureanswer = number1 * number2; 

      if (answer == tureanswer){ 
       System.out.println("Correct"); 
      } 
      else 
       System.out.println("Wrong. The correct answer is "+ tureanswer); 
     } 
    }while(userinput !=3); 
} 
} 

我得到下面的输出，

1: Multiplication 
2: Addition 
3: Exit 
Please choose a number: 1 
What is 9 + 1 12 
Wrong,correct answer is 10 
What is 9 + 1 

不过，我需要这样的事情， （提示用户选择号码不是what is 9 + 1）

1: Addition 
2: Multiplication 
3: Exit 
Please choose a number: 1 
What is 9 + 1 12 
Wrong,correct answer is 10 

1: Addition 
2: Multiplication 
3: Exit 
Please choose a number: 

我在do声明中做错了什么？任何想法将不胜感激！

Answer 1

它在我看来像你需要移动do {了几行。

只有do {和while之间的部分得到重复，并且您需要包括询问用户需要哪种类型的问题并生成随机数。

然而，你将需要之前do声明userInput，如果你想用它作为while条件。

int userInput; 

    do { 
     System.out.print("Please choose a number: "); 

     userinput = input.nextInt(); 

     // Generate two random numbers 
     int number1 = (int)(Math.random() * 10); 
     int number2 = (int)(Math.random() * 10); 

     if (userinput == 1) { 

      // and so on ... 

Answer 2

添加以下你做线，而

System.out.println("1: Multiplication"); 
System.out.println("2: Addition"); 
System.out.println("3: Exit"); 

System.out.print("Please choose a number: "); 

int userinput = input.nextInt(); 
int number1 = (int)(Math.random() * 10); 
int number2 = (int)(Math.random() * 10); 

我也建议你在做使用开关，同时，因为它更实用的比，如果其他