时间戳

首页 > 解决方案 > 在java中的while循环之前添加程序退出

java - 在java中的while循环之前添加程序退出

问题描述

如果在循环开始之前输入 -1 以终止循环，我无法让程序停止并显示下面的消息。如果输入了不同的整数，该程序也不会流入 while 循环。我似乎把我的大括号放错了地方，因为最后两个出错了。

public static void main(String[] args)
{
    double score;
    double total = 0.0;
    double average;
    int scoreCount = 0;

    // create the Scanner object. Name it stdin
    Scanner stdin = new Scanner(System.in);

    // title at the top of the output
    System.out.println (" score report");;

    do{
    //   read the first score
        System.out.printf ("Enter a score  (1-100, -1 to quit)"
            + ": ", scoreCount);
        score = stdin.nextDouble();

        if (score == -1)
        {
            System.out.println ("Nothing entered.");
        }           
    while((score = stdin.nextDouble()) != -1.0)
    {              
        if (score<-1 || score>100)
        {
        System.out.println ("Illegal score.  Try again");
        System.out.printf ("Enter a score  (1-100, -1 to quit)"
              + ": ", scoreCount);
        }
        else
        {
            System.out.printf ("Enter a score  (1-100, -1 to quit)"
              + ": ", scoreCount); 
            scoreCount++;
            total += score;
        }        
           // end of for loop
    average = total / scoreCount;       //equation
    System.out.printf ("\nThe average score for %d students is %8.2f\n",
                          scoreCount, average); 
    }
} // end of main

} // 类定义结束

标签： java

解决方案

在 do 循环结束时需要一个“while”条件。这就是为什么它被称为 do-while 循环。如果没有 while 条件，您应该会收到编译时错误。这是一个例子：

double score;
double total = 0.0;
double average;
int scoreCount = 0;

// create the Scanner object. Name it stdin
Scanner stdin = new Scanner(System.in);

// title at the top of the output
System.out.println ("Score Report");

 do{
  //   read the first score
      System.out.println("Enter a score (0-100 or -1 to quit)" 
            + ": " + scoreCount);
      score = stdin.nextDouble();//Retrieve the score.

      if(score == -1) {
        System.out.println("Bye!");
       }

      if (score<-1 || score>100)//Here is the if statement that makes the user enter another score if it is illegal
      {
        System.out.println("Illegal score.  Try again");
        continue; //A continue statement will start the loop over again from the top!
      }
      else if(score >= 0 && score <= 100 && score != -1)
      {

            scoreCount++;
            total += score;
       }        
      // end of for loop
      average = total / scoreCount;       //equation
      System.out.println();
      System.out.printf ("\nThe average score for %d students is %8.2f\n",
                          scoreCount, average); 
      System.out.println();
}while(score != -1); //Runs "while" the score != -1

以下是该程序可能输出的示例：

Score Report
Enter a score (0-100 or -1 to quit): 0
50.0


The average score for 1 students is    50.00

Enter a score (0-100 or -1 to quit): 1
50.0


The average score for 2 students is    50.00

Enter a score (0-100 or -1 to quit): 2
-90
Illegal score.  Try again
Enter a score (0-100 or -1 to quit): 2
50.0


The average score for 3 students is    50.00

Enter a score (0-100 or -1 to quit): 3
-1
Bye!


The average score for 3 students is    50.00

正如您在此处看到的，您的 if 语句更改为：

if (score<-1 || score>100)//Here is the if statement that makes the user enter another score if it is illegal
        {
        System.out.println("Illegal score.  Try again");
        continue;
        }

continue 语句将强制循环从头开始，而不执行循环中的其余代码。这将帮助您避免无效输入。在 do 循环结束时，您还需要这个 while 条件：

 }while(score != -1);

现在循环只会在分数不等于负 1 时继续。如果分数等于 -1，您还可以在代码中通知用户他们正在退出程序：

if(score == -1) {
            System.out.println("Bye!");
        }

如果输入的数字在 0 到 100 的范围内，您可以将 else 语句更改为 else if 语句以执行，否则 -1 条目将被计为分数：

else if(score >= 0 && score <= 100 && score != -1)
        {

            scoreCount++;
            total += score;
        }        
           // end of for loop

你也没有像你说的那样退出你的循环。每次迭代循环时都会计算平均值。将显示平均值的代码放在循环之外：

}while(score != -1);
    average = total / scoreCount;       //equation
    System.out.println();
    System.out.printf ("\nThe average score for %d students is %8.2f\n",
                      scoreCount, average);

现在输出将如下所示：

Score Report
Enter a score (0-100 or -1 to quit): 0
50.0
Enter a score (0-100 or -1 to quit): 1
70.0
Enter a score (0-100 or -1 to quit): 2
90.0
Enter a score (0-100 or -1 to quit): 3
-1
Bye!


The average score for 3 students is    70.00

如果您希望仅在输入 -1 作为第一个选项时显示消息，请执行以下操作：

if(score == -1 && scoreCount == 0) {
            System.out.println("Bye!");
        }

推荐阅读