我可以在两个连续的 if 语句之后执行 for 循环吗？ [复制]

Question

我正在开发一个程序，该程序必须在执行两个 for 循环（一个用于输入的成绩总和，一个用于最高和最低成绩）之前检查某些条件（如果未执行则发出错误消息）而且我不确定如何对它们进行排序。

我的代码也让我收到此错误 -->线程“main”java.lang.ArrayIndexOutOfBoundsException 中的异常：0，我不确定如何修复该错误

如果有人可以帮助我制作正确序列的骨架，我将不胜感激！

这是我的代码（我知道它看起来很疯狂，抱歉我正在学习！）：

import java.util.Scanner;

public class Homework {

    public static void main (String[] args) {
        Scanner input = new Scanner(System.in);
        int numberOfMarks, average, sum, total, mark;
        numberOfMarks = 0;
        int [] marks = new int[numberOfMarks];
        int smallest, largest;
        //System.out.println("Enter number of marks: ");
        numberOfMarks = input.nextInt();
        if(numberOfMarks<0) {
        System.out.println("Number of marks must be greater than 0!!");
        }
        //System.out.println("Enter "+numberOfMarks+"marks: ");
        mark = input.nextInt();
        if(mark<0) {
            System.out.println("Negative marks not allowed!!!");
        } else if(mark>100) {
            System.out.println("Marks above 100% not allowed!!!");
        }  
        sum = 0;
        for(int i = 0; i < marks.length; i++) {
            sum += marks[i];
        }
        smallest=marks[0];
        largest=marks[0];
        for(int i=1;i<marks.length;i++) {       
            if(marks[i]>largest) {
                largest=marks[i];
            } else if(marks[i]<smallest) {
                smallest=marks[i];
            }
            average = sum/numberOfMarks;
            System.out.println("Highest Mark = "+largest);
            System.out.println("Lowest Mark = "+smallest);
            System.out.println("Average = "+average);
        }
    }
}

Answer 1

你可以试试这个：

import java.util.Arrays;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner in = new Scanner(System.in);
        int numberOfSubjects, sum;
        numberOfSubjects = 0;

        System.out.print("Enter the total number of subjects: ");
        numberOfSubjects = in.nextInt();

        if(numberOfSubjects < 0){
        System.out.println("Number of marks must be greater than 0!!");
        }
        else {
            int []marks = new int[numberOfSubjects];
            sum = 0;

            System.out.print("Enter the marks: ");
            // add condition inside for loop for marks not less than 1 or greater than 100 
            for(int i=0; i<marks.length; i++) {
                    marks[i] = in.nextInt();
            }

            // calculate total
            for(int i = 0; i < marks.length; i++){
                sum += marks[i];
            }

            // sort marks
            Arrays.sort(marks);

            System.out.println("Total: " + sum);
            System.out.println("Average: " + sum/numberOfSubjects);
            System.out.println("Minimum: " + marks[0]);
            System.out.println("Maximum: " + marks[marks.length-1]);
        }
    }
}

代码流应该是这样的。甚至您可以在阅读分数时添加分数条件（不小于1或大于100）。

Answer 2

问题出在逻辑上，见下面的 cmets

import java.util.Scanner;

public class Homework {

 public static void main(String[] args) {

  Scanner input = new Scanner(System.in);

  int numberOfMarks, average, sum, total, mark;
  numberOfMarks = 0;
  /*there you are creating empty array
    you told marks should have length of value numberOfMarks, but 
    numberOfMarks is equal to zero at this time
  */
  int[] marks = new int[numberOfMarks]; 
  int smallest, largest;

  //System.out.println("Enter number of marks: ");
  numberOfMarks = input.nextInt();

 /*
   not interesting conditions checking... 
 */

  for (int i = 0; i < marks.length; i++) {
   /*
     There you are trying to access 1st element of marks
       - indexing from zero, as usual
     But there is no first element, array has zero length, zero elements
      Ok, you told array should have length of numberOfMarks, but it was 
       when value was zero, so if you will change numberOfMarks later, it 
        has no impact on the length of array
   */
   sum += marks[i];
  }

  /*
    stats computing, not important
  */

 }

}

所以，一旦你得到用户输入的标记数，你就可以“重新创建”——重新分配/重新定义数组，就像以前一样 marks = new int[numberOfMarks];

你的情况如下

//System.out.println("Enter number of marks: ");
numberOfMarks = input.nextInt();

使用数组长度变量并不意味着它会是有界的，所以如果数组长度变量（在这种情况下numberOfMarks）在使用后会发生变化，那么数组长度将保持不变