for循环结构

Question

该程序将通过提示使用 for 循环计算 4 门考试的平均成绩 考试成绩的用户，一次一个，然后计算平均值并显示结果。

public class ExamsFor4 {

public static void main(String[] arguments) {


int inputNumber; // One of the exams input by the user.
int sum = 0;     // The sum of the exams.
int i;       // Number of exams.
Double Avg;      // The average of the exams.

TextIO.put("Please enter the first exam: ");        // get the first exam.
inputNumber = TextIO.getlnInt();    

for ( i = 1; i <= 4; i++ ) {  

    sum += inputNumber;                 // Add inputNumber to running sum.
    TextIO.put("Please enter the next exam: ");     // get the next exam.   
    inputNumber = TextIO.getlnInt();

        if (i == 4) {
            Avg = ((double)sum) / i;
            TextIO.putln();
            TextIO.putln("The total sum for all " + i +" exams is " + sum);
            TextIO.putf("The average for the exams entered is %1.2f.\n", Avg);
            break;

        }
} 

}   // end main ()
}  // end class ExamsFor4

我的结果：

Please enter the first exam: 100
Please enter the next exam: 99
Please enter the next exam: 98
Please enter the next exam: 97
Please enter the next exam: 96
The total sum for all 4 exams is 394
The average for the exams entered is 98.50.

这将是正确的，除了最后一个打印输出：'Please enter the next exam: 96' 我尝试将 IF 语句放在“sum”行和TextIO.put 'Enter next exam' 之间，但这会将其隔离。

感谢，来自程序员世界中的网络老兄陷阱。

Answer 1

您遇到了所谓的逐一错误，再加上您不必要地对循环逻辑进行卷积。

关于循环，我推荐两件事：

• 不要循环for (int i = 1; i <= N; i++)；这是非典型的
  • 做for (int i = 0; i < N; i++);比较典型
• 不要检查最后一次迭代来做某事，而是重构并将其置于循环之外

相关问题

• What is exactly the off-by-one errors in the while loop?

另见

• Wikipedia/Off-by-one error

---

开启Double Avg

在 Java 中，变量名以小写字母开头。此外，Double 是一个引用类型，即原始 double 的框。只要有可能，你应该更喜欢double 而不是Double

另见

• Java Language Guide/Autoboxing
• JLS 5.1.7 Boxing Conversion 和 5.1.8 Unboxing Conversion
• Effective Java 2nd Edition，Item 49：Prefer primitives to boxed primitives

相关问题

• What is the difference between an int and an Integer in Java/C#?
• Java: What’s the difference between autoboxing and casting?
• Why does int num = Integer.getInteger(“123”) throw NullPointerException?
• Why does autoboxing in Java allow me to have 3 possible values for a boolean?
• Is it guaranteed that new Integer(i) == i in Java?（是的！！！）
• When comparing two Integers in Java does auto-unboxing occur? （不！！！）
• Java noob: generics over objects only?（是的，很遗憾）

---

重写

这是一种重写代码使其更具可读性的方法。我使用java.util.Scanner，因为我不认为TextIO 是标准的，但本质保持不变。

import java.util.*;

public class ExamsFor4 {
    public static void main(String[] arguments) {
        Scanner sc = new Scanner(System.in);
        final int NUM_EXAMS = 4;
        int sum = 0;

        for (int i = 0; i < NUM_EXAMS; i++) {
            System.out.printf("Please enter the %s exam: ",
                (i == 0) ? "first" : "next"
            );
            sum += sc.nextInt();
        }
        System.out.printf("Total is %d%n", sum);
        System.out.printf("Average is %1.2f%n", ((double) sum) / NUM_EXAMS);
    }
}

一个示例会话如下：

Please enter the first exam: 4
Please enter the next exam: 5
Please enter the next exam: 7
Please enter the next exam: 9
Total is 25
Average is 6.25

注意：

• 只声明必要的变量
  • 循环索引仅在循环本地
• 没有杂乱无章的 cmets
  • 相反，应专注于编写清晰、简洁、易读的代码
• 如果做某事final 有意义，那就去做吧
  • Java 中的常量都是大写的

相关问题

• Why does (360 / 24) / 60 = 0 in Java
  • 因为它执行整数除法。这就是为什么在上面的代码中在除法之前强制转换为(double) 是必要的，以便它执行浮点除法。
• How does the ternary operator work?
  • 这是上面代码中的?:运算符，也称为条件运算符。
  • 另见：JLS 15.25 Conditional Operator ?:

Answer 2

将结束条件更改为严格小于 4，并将打印出总和平均值的代码放在循环之外。

Answer 3

您可能应该将 if 语句放在 for 循环之外。这样你就不需要 if 语句。其次，循环中的语句应该是

public class ExamsFor4 {

public static void main(String[] arguments) {


int inputNumber; // One of the exams input by the user.
int sum = 0;     // The sum of the exams.
int i;       // Number of exams.
Double Avg;      // The average of the exams.

TextIO.put("Please enter the first exam: ");        // get the first exam.
inputNumber = TextIO.getlnInt();    

for ( i = 1; i < 4; i++ ) {  

    sum += inputNumber;                 // Add inputNumber to running sum.
    TextIO.put("Please enter the next exam: ");     // get the next exam.   
    inputNumber = TextIO.getlnInt();
} 

Avg = ((double)sum) / i;
TextIO.putln();
TextIO.putln("The total sum for all " + i +" exams is " + sum);
TextIO.putf("The average for the exams entered is %1.2f.\n", Avg);
break;

}   // end main ()
}

Answer 4

只需对代码进行一些更改即可使其正常工作。但是您应该遵循一些答案中提出的更简洁的方法。

public class ExamsFor4 {

  public static void main(String[] arguments) {
    int inputNumber; // One of the exams input by the user.
    int sum = 0;     // The sum of the exams.
    int i;       // Number of exams.
    double Avg;      // The average of the exams.

    TextIO.put("Please enter the first exam: ");        // get the first exam.
    inputNumber = TextIO.getlnInt();    
    sum += inputNumber;

    for ( i = 1; i < 4; i++ ) {  

      TextIO.put("Please enter the next exam: ");     // get the next exam.   
      inputNumber = TextIO.getlnInt();
      sum += inputNumber;                 // Add inputNumber to running sum.

    } 

    Avg = ((double)sum) / i;
    TextIO.putln();
    TextIO.putln("The total sum for all " + i +" exams is " + sum);
    TextIO.putf("The average for the exams entered is %1.2f.\n", Avg);

  }   // end main ()
}  // end class ExamsFor4

Answer 5

import java.util.Scanner;
public class ExamsFor4 {

public static void main(String[] arguments) {

    int sum = 0; // The sum of the exams.
    int i = 1; // Number of exams.
    double avg = 0; // The average of the exams.

    Scanner in = new Scanner(System.in);
    System.out.print("Please enter the first exam: ");
    sum += in.nextInt();
    i++;
    while(i<=4){
        System.out.print("Please enter the next exam: ");
        sum += in.nextInt();
        if(i==4)
            break;// this line is so that it wont increment an extra time.
        i++;
    }
    System.out.println("The total sum for all " + i +" exams is " + sum);
    avg = ((double)sum/i);
    System.out.println("The average for the exams entered is" + avg);
} // end main ()
} // end class ExamsFor4