用于运行/停止程序的 for 循环答案

【问题标题】：a for loop to run/stop program用于运行/停止程序的 for 循环
【发布时间】：2013-02-01 22:11:28
【问题描述】：

我正在编写一个比较两个整数的程序，我希望程序运行到用户感到疲倦并想要退出，为此用户将输入 q 退出。我想编写一个while循环来比较两个字符，一个是用户输入的字符，另一个是分配给它的'q'。但是，当我输入 q 时，我的程序崩溃了，为什么会这样，我该如何解决它

import java.io.IOException;
import java.util.Scanner;


public class numComp {

public static void main(String[] args) {

    Scanner in = new Scanner(System.in);
    int a, b; 
    char key  = 'q';
    System.out.println("enter 'q' to quit program and any other key to start it");

    char btn = 0;
    try {
        btn = (char) System.in.read();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    while (btn != key){
    System.out.println("enter two numbers to compare them");
    System.out.println("please enter first number:");
    a = in.nextInt();
    System.out.println("please enter second number:");
    b = in.nextInt();

    if (a==b)
        System.out.println("the numbers you entered are the same");
    else if (a>b)
        System.out.println("your first number is greater then your second number by "+ (a-b));
    else
        System.out.println("your first number is smaller then your second number by "+ (b-a));
    }

}

}

【问题讨论】：

用户应该在哪里输入'q'？因为在我看来，您只允许输入数字。

标签： java for-loop char compare

【解决方案1】：

这是简化程序。

public static void main(String[] args){
    // Scanner
    Scanner s = new Scanner(System.in);
    // Enter the program
    System.out.println("enter 'q' to quit program and any other key to start it");
    int a, b;
    try {
        char key;
        while ((key = s.next().charAt(0))!='q'){
            System.out.println("enter two numbers to compare them");
            System.out.println("please enter first number:");
            a = s.nextInt();
            System.out.println("please enter second number:");
            b = s.nextInt();

            if (a==b)
                System.out.println("the numbers you entered are the same");
            else if (a>b)
                System.out.println("your first number is greater then your second number by "+ (a-b));
            else
                System.out.println("your first number is smaller then your second number by "+ (b-a));
        }
    } catch (Exception e){ e.printStackTrace(); }
}

【讨论】：

【解决方案2】：

你的循环应该是这样的：

try{  
    btn = (char) System.in.read();
    while (btn != key){
    System.out.println("enter two numbers to compare them");
    System.out.println("please enter first number:");
    a = in.nextInt();
    System.out.println("please enter second number:");
    b = in.nextInt();

   if (a==b)
      System.out.println("the numbers you entered are the same");
  else if (a>b)
      System.out.println("your first number is greater then your second number by "+ (a-b));
  else
     System.out.println("your first number is smaller then your second number by "+ (b-a));

   System.out.println("enter 'q' to quit program and any other key to start it again");
   btn = (char) System.in.read();
  } // END OF WHILE LOOP
} catch (IOException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
}

另请注意，您需要在 while 循环结束之前再次从用户那里获取输入。

【讨论】：

【解决方案3】：

那是因为在 while 循环中，您正在扫描整数，但“q”是一个字符。您需要让用户有机会阅读 btn inside while 循环。

【讨论】：

【解决方案4】：

检查时需要更改btn。您只在循环之前设置一次，并且永远不会更新。

例外是因为

a = in.nextInt();

当您输入char 时，您会尝试读取int。

您需要在循环末尾添加如下内容：

btn = (char) System.in.read();

【讨论】：