为什么我无法获得分类的输出？

why i cant get the output for categorize?

提问人： 提问时间：10/14/2023 最后编辑：Iłya Bursov 更新时间：10/15/2023 访问量：67

问：

我必须制作一个 Java 程序来接收学生数据并停在 -1，然后显示成绩数及其平均值，最后，它将显示类别 A、B、C、D 的成绩。此代码仅在显示类别时出现错误。我需要帮助。在其中，我将输入所需的输出

import java.util.Scanner;

public class Grades {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.println("enter 5 grades and then -1 to quit!");
        System.out.print("enter grade:");
        double grade = input.nextDouble();
        double total = 0;
        int count = 0;
        int A = 0;
        int B = 0;
        int C = 0;
        int D = 0;
        int F = 0;

        while (grade != -1) {
            total = total + grade;
            System.out.print("enter grade:");
            grade = input.nextDouble();
            count++;
        }

        System.out.println("the number of grades= " + count);
        System.out.println("Average: " + total / count);

        if (grade >= 90 && grade <= 100) {
            A++;
        } else if (grade >= 80 && grade <= 89) {
            B++;
        } else if (grade >= 70 && grade <= 79) {
            C++;
        } else if (grade >= 60 && grade <= 69) {
            D++;
        } else if (grade >= 0 && grade <= 59) {
            F++;
        }
        
        System.out.println("number of A grades :" + A);
        System.out.println("number of B grades :" + B);
        System.out.println("number of C grades :" + C);
        System.out.println("number of D grades :" + D);
        System.out.println("number of F grades :" + F);
    }
}

输出应为：

输入等级：90 输入等级：99 输入等级：97 输入等级：98 输入等级：87 输入等级：-1 等级数= 5 平均：94.2

A级总数：4 B级总数：1 C级总数：0 D级总数：0 F级总数：0

但相反，我得到了这个：

输入等级：90 输入等级：99 输入等级：97 输入等级：98 输入等级：87 输入等级：-1 等级数= 5 平均：94.2

A级总数：0 B级总数：0 C级总数：0 D级总数：0 F级总数：0

有人可以告诉我为什么它不起作用吗？

java if-statement 输入 while 循环

评论

0赞 Iłya Bursov 10/14/2023
循环后变量的值是多少？gradewhile (grade!=-1)

答：

2赞 Jeet Kumar 10/14/2023 #1

代码的问题在于，您在 while 循环完成后检查成绩，这意味着该变量在该点包含 -1 的值，并且您只计算成绩类别的一个值。在阅读成绩时，您应该检查循环中的类别。以下是更正后的代码：grade

import java.util.Scanner;

public class Grades {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.println("Enter 5 grades and then -1 to quit!");
        double total = 0;
        int count = 0;
        int A = 0;
        int B = 0;
        int C = 0;
        int D = 0;
        int F = 0;

        while (true) {
            System.out.print("Enter grade (or -1 to quit): ");
            double grade = input.nextDouble();

            if (grade == -1) {
                break;  // Exit the loop when -1 is entered
            }

            total += grade;
            count++;

            if (grade >= 90 && grade <= 100) {
                A++;
            } else if (grade >= 80 && grade <= 89) {
                B++;
            } else if (grade >= 70 && grade <= 79) {
                C++;
            } else if (grade >= 60 && grade <= 69) {
                D++;
            } else if (grade >= 0 && grade <= 59) {
                F++;
            }
        }

        System.out.println("The number of grades = " + count);
        System.out.println("Average: " + total / count);

        System.out.println("Number of A grades: " + A);
        System.out.println("Number of B grades: " + B);
        System.out.println("Number of C grades: " + C);
        System.out.println("Number of D grades: " + D);
        System.out.println("Number of F grades: " + F);
    }
}

使用此代码，您可以在循环中收到每个成绩时检查成绩类别，它将产生所需的输出。

0赞 nokla 10/14/2023 #2

当您退出循环并到达零件时，值为 因此，任何条件都不会为真。if-elsegrade-1

您需要将零件移动到循环中：if-elsewhile

    while (grade!=-1){
    total += grade;

    if(grade>=90 && grade<=100){
        A++;}
    else if(grade>=80 && grade<=89){
        B++;}
    else if(grade>=70 && grade<=79){
        C++;}
    else if(grade>=60 && grade<=69){
        D++;}
    else if(grade>=0 && grade<=59){
        F++;}
    count++;
    System.out.print("enter grade:");
    grade=input.nextDouble();
    }

输出：

enter 5 grades and then -1 to quit!
enter grade:90
enter grade:99
enter grade:97
enter grade:98
enter grade:87
enter grade:-1
the number of grades= 5
Average: 94.2
number of A grades :4
number of B grades :1
number of C grades :0
number of D grades :0
number of F grades :0

编辑：

import java.util.Scanner;
public class Grades {
public static void main(String []args){   
Scanner input = new Scanner(System.in);

 System.out.println("enter 5 grades and then -1 to quit!");
 System.out.print("enter grade:");
 double grade=input.nextDouble();
 double total=0;
 int count=0;
 int A= 0;
 int B= 0;
 int C = 0;
 int D= 0;
 int F = 0;
 
 
while (grade!=-1){
    total += grade;
    if(grade>=90 && grade<=100){
        A++;}
    else if(grade>=80 && grade<=89){
        B++;}
    else if(grade>=70 && grade<=79){
        C++;}
    else if(grade>=60 && grade<=69){
        D++;}
    else if(grade>=0 && grade<=59){
        F++;}
    count++;
    System.out.print("enter grade:");
    grade=input.nextDouble();
}
    
    
 System.out.println("the number of grades= "+ count);
 System.out.println("Average: " + total/count);
 

System.out.println("number of A grades :"+ A);
System.out.println("number of B grades :"+ B);
System.out.println("number of C grades :"+ C);
System.out.println("number of D grades :"+ D);
System.out.println("number of F grades :"+ F);
    
}   
}

评论

0赞 Iłya Bursov 10/14/2023
如果部分应该在之前，否则将跳过第一个值读取（在 main 的最开头读取）nextDouble
0赞 nokla 10/14/2023
@I łyaBursov 是的，我只是忘记保存编辑:)
0赞 10/14/2023
感谢您的回答，我真的很高兴您帮助了我！我做了你告诉我的和它的作品！但是有一个错误，它给了我 6 个等级，而我以 -1 输入了 5 个等级，那么我该如何解决这个问题？
0赞 nokla 10/14/2023
@sera 嗨，我附上了输出..
0赞 10/14/2023
很抱歉打扰了，但它仍然给了我 6 而不是 5 <\\3
1赞 Reilas 10/14/2023 #3

"...此代码仅在显示类别时出现错误。...

。有人可以告诉我为什么它不起作用吗？

发生这种情况的原因是您正在检查 grade 的值，在循环之后，该值为 −1。

此外，您还应该统一收集输入值。
并且，重构等级 if 语句。

Scanner input = new Scanner(System.in);


System.out.println("enter 5 grades and then -1 to quit!");
double grade;
double total=0;
int count=0;
int A= 0;
int B= 0;
int C = 0;
int D= 0;
int F = 0;
boolean exit = false;

do {
    System.out.print("enter grade:");
    grade=input.nextDouble();
    if (grade == -1) exit = true;
    else {
        total = total + grade;
        count++;
        if(grade>=90) A++;
        else if(grade>=80) B++;
        else if(grade>=70) C++;
        else if(grade>=60) D++;
        else F++;
    }
} while (!exit);


System.out.println("the number of grades= "+ count);
System.out.println("Average: " + total/count);


System.out.println("number of A grades :"+ A);
System.out.println("number of B grades :"+ B);
System.out.println("number of C grades :"+ C);
System.out.println("number of D grades :"+ D);
System.out.println("number of F grades :"+ F);

输出

enter 5 grades and then -1 to quit!
enter grade:90
enter grade:80
enter grade:70
enter grade:-1
the number of grades= 3
Average: 80.0
number of A grades :1
number of B grades :1
number of C grades :1
number of D grades :0
number of F grades :0

评论

0赞 10/14/2023
谢谢kkkkk yoooouuu，我哭了，它!!

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