如果输入-1以终止循环，则无法让程序停止并在下面显示消息。如果输入了不同的整数，该程序也将不会进入while循环。我似乎将大括号放到了某个地方，因为最后两个错误。
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
} //类定义的结尾
答案 0 :(得分：0)
根据我的理解，该问题有一个简单的解决方案。要退出循环，只需使用import java.util.*;
import java.io.*;
/**
* Counts composition of children's sexes among nuclear families.
*
* @author Thomas Morey
* @version 10/7/18
*/
public class Family
{
public static void main() throws IOException{
File read = new File("C:/Users/tdmor/Desktop/Misc/School/AP Comp Science/Recources/maleFemaleInFamily.txt"); //entire file path necisary?
Scanner inf = new Scanner(read); //stands for in file
String family;
int quan;
int i = 1;
while(inf.hasNext()){
family = inf.next();
String famNum/*increment here*/ = family; //create a variable with the int "i" appended to the end of the variable name to represent how many families there are.
quan = i;
System.out.println(family);
i++;
}
}
}
：
break此外，根据代码，实际上并不需要“ do”语句。只需使用常规的while循环即可。
答案 1 :(得分：0)
在do循环的末尾需要一个“ while”条件。这就是为什么将其称为“ do-while”循环的原因。没有while条件，您应该得到一个编译时错误。这是一个示例：
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
以下是该程序可能的输出示例：
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
如您在此处看到的，如果语句更改为：
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，而无需在循环中执行其余代码。这将帮助您避免输入无效。 在do循环的最后，您还需要while条件：
}while(score != -1);
现在，仅当分数不等于负1时，循环才会继续。如果分数等于-1，您还可以告知用户他们正在您的代码中退出程序：
if(score == -1) {
System.out.println("Bye!");
}
如果输入的数字在0到100之间，否则您可以将else语句更改为else if语句以执行，否则-1项将被计为分数：
else if(score >= 0 && score <= 100 && score != -1)
{
scoreCount++;
total += score;
}
// end of for loop
您也不会退出循环，就像您说自己在上面一样。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
如果只希望在输入-1作为第一个选项时显示一条消息，请执行以下操作：
if(score == -1 && scoreCount == 0) {
System.out.println("Bye!");
}
答案 2 :(得分：0)
发布的代码将无法编译。这是一个正确的函数，可以输入一堆从0到100的数字并计算平均值。输入-1时，程序将退出。我已经在代码中添加了注释。
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");
//Request the first score
System.out.printf ("Enter a score %d (1-100, -1 to quit)"
+ ": ", scoreCount+1);
//read the first score
score = stdin.nextDouble();
do{
//check the entered score and decide what to do.
if (score == -1)
{
System.out.println ("Nothing entered.");
break;
} else if (score<-1 || score>100)
{
System.out.println ("Illegal score. Try again");
System.out.printf ("Enter a score %d (1-100, -1 to quit)"
+ ": ", scoreCount+1);
}
else
{
scoreCount++;
total += score;
// The entered score is good ask for the next one
System.out.printf ("Enter a score %d (1-100, -1 to quit)"
+ ": ", scoreCount+1);
}
}while((score = stdin.nextDouble()) != -1.0); // Here we read the input.
// end of the program.
average = total / scoreCount; //equation
System.out.printf ("\nThe average score for %d students is %8.2f\n",
scoreCount, average);
} // end of main