数组的总和和平均值

Question

我正在为我的大学课程研究一个数组问题，我正在尝试找到一个数组的总和和平均值。这是我到目前为止的代码。

public class Module55
{
   public static void main(String args[])
   {

   //declare the array to have 10 items for 10 weeks
   //also declare sum as an int and average as a double to accommodate for decimal points

      int[] weeks = new int[10];
      int sum = 0;
      double average = 0;

   //declare the array values

      weeks[0]= 2;
      weeks[1]= 4;
      weeks[2]= 8;
      weeks[3]= 10;
      weeks[4]= 14;
      weeks[5]= 16;
      weeks[6]= 20;
      weeks[7]= 22;
      weeks[8]= 24;
      weeks[9]= 26;

   // determine sum of the array values

     for (int index = 0; index < weeks.length; index++) weeks[index] = index;
        sum = sum + weeks[index];
        System.out.println("The total miles ran in 10 weeks is " + sum);

   // determine the average of the array values

     if (weeks.length != 0)
        average = sum / weeks.length;
     else
        average = 0;

     System.out.println("The average of the miles ran in 10 weeks is " + average);
     }
}

我知道平均值有效，但我坚持总和。我遇到的问题是我似乎无法初始化数组中的值，以便为它们提供总和。我做错了什么或者我错过了什么？

Answer 1

您的代码中有两个问题；

A) For 循环赋值

第一个作业不用做，把sum加到week[index]上就可以了；

    for (int index = 0; index < weeks.length; index++)
        sum = sum + weeks[index];

B) 计算平均值

Sum 被定义为int，它是一个原始整数，因此，将整数除以整数，输出是一个不精确的整数。除法 (45/10) 的输出被转换为整数，然后分配给 double，四舍五入为 4，然后再次转换为 double，结果为 '4.0'。

为避免这种不精确的结果，请将 sum 转换为如下所示的 double；

average = (double)sum / weeks.length;

您的代码的更正版本如下；

演示

public class Module55 {
    public static void main(String args[]) {

        // declare the array to have 10 items for 10 weeks
        // also declare sum as an int and average as a double to accommodate for
        // decimal points

        int[] weeks = new int[10];
        int sum = 0;
        double average = 0;

        // declare the array values

        weeks[0] = 2;
        weeks[1] = 4;
        weeks[2] = 8;
        weeks[3] = 10;
        weeks[4] = 14;
        weeks[5] = 16;
        weeks[6] = 20;
        weeks[7] = 22;
        weeks[8] = 24;
        weeks[9] = 26;

        // determine sum of the array values
        for (int index = 0; index < weeks.length; index++)
            sum = sum + weeks[index];

        System.out.println("The total miles ran in 10 weeks is " + sum);

        // determine the average of the array values
        if (weeks.length != 0)
            average = (double)sum / weeks.length;
        else
            average = 0;

        System.out.println("The average of the miles ran in 10 weeks is " + average);
    }
}

输出

The total miles ran in 10 weeks is 146
The average of the miles ran in 10 weeks is 14.6

以及范围说明

关于范围的最后一点说明，请查看此代码；

 for (int index = 0; index < weeks.length; index++)
    weeks[index] = index;
    sum = sum + weeks[index];
    System.out.println("The total miles ran in 10 weeks is " + sum);

在for-loop中，由于没有使用括号，因此编译器在循环的scope中只考虑for-loop下的第一条语句。这就是为什么对于下一行，编译器会给出关于索引的错误，因为索引是在 for-loop 的 scope 内定义的。

Answer 2

您需要在 for 循环中使用方括号。目前你的代码是这样评估的：

for (int index = 0; index < weeks.length; index++) 
{
    weeks[index] = index;
}
sum = sum + weeks[index];
System.out.println("The total miles ran in 10 weeks is " + sum);

你希望你的代码像这样评估

for (int index = 0; index < weeks.length; index++) 
{
    weeks[index] = index; //logical issue, what does this line achieve?
    sum = sum + weeks[index];
}
System.out.println("The total miles ran in 10 weeks is " + sum);

这至少会解决您的程序问题，但您仍然需要查看您的逻辑。尝试使用断点来调试您的代码。

Answer 3

在 Java 8 中实现此目的的一个非常简单的方法是使用内置机制来收集统计信息：

int[] weeks = {3, 4, 6, 9, 10};
IntSummaryStatistics stats = IntStream.of(weeks).summaryStatistics();
System.out.println("sum = " + stats.getSum() + "; average = " + stats.getAverage());

Answer 4

for (int i = 0;i < weeks.length) {
    sum += weeks[i];
}

System.out.println("Sum is:" + sum);

Answer 5

首先，您根本不需要这行weeks[index] = index;。 对于平均值，如果您想将平均值设为双倍，您必须将总和设为两倍，因为您已将总和声明为 int。

public class Module55
{
   public static void main(String args[])
   {

   //declare the array to have 10 items for 10 weeks
   //also declare sum as an int and average as a double to accommodate for decimal points

      int[] weeks = {2,4,8,10,14,16,20,22,24,26};
      int sum = 0;
      double average = 0;

   // determine sum of the array values

     for (int index = 0; index < weeks.length; index++) 
         //weeks[index] = index;
         sum = sum + weeks[index];
         System.out.println("The total miles ran in 10 weeks is " + sum);

   // determine the average of the array values

     if (weeks.length != 0)
        average = (double)sum / weeks.length;
     else
        average = 0;

     System.out.println("The average of the miles ran in 10 weeks is " + average);
     }
}

10 周内跑的总里程为 146 英里

10 周的平均跑步里程为 14.6 英里

Answer 6

像这样将一个数字数组相加并除以 n 以获得平均值不会得到正确的值 - 您不应该使用整数除法来计算平均值。 此外，这种方法可能适用于所示示例，但通常不适用。例如，尝试使用此代码查找这两个值的平均值：(INT_MAX-6) 和 (INT_MAX-2)。

Answer 7

更正后的代码。在计算平均值时，您将变量加倍，否则您将得到平均值作为整数

public class Mod55 {

    public static void main(String args[]) {

        //declare the array to have 10 items for 10 weeks
        //also declare sum as an int and average as a double to accommodate for decimal points
        int[] weeks = new int[]{2, 4, 8, 10, 14, 16, 20, 22, 24, 26};
        int sum = 0;
        double average = 0;

        // determine sum of the array values
        for (int index = 0; index < weeks.length; index++) {
            sum += weeks[index];
        }
        System.out.println("The total miles ran in 10 weeks is " + sum);

        // determine the average of the array values
        if (weeks.length != 0) {
            average = (double)sum / weeks.length;
        } else {
            average = 0;
        }

        System.out.println("The average of the miles ran in 10 weeks is " + average);
    }
}

Java8 你可以像这样实现同样的事情。

        int[] weeks = new int[]{2, 4, 8, 10, 14, 16, 20, 22, 24, 26};
        int sum = Arrays.stream(weeks)
                 .sum();
        double average = Arrays.stream(weeks).average().orElse(0);

Answer 8

您可以使用 lambdas 找到这个方便。代码看起来像这样。

int weeks[] = {1,2,3,4};
List<Integer> asd = IntStream.of(weeks).boxed().collect(Collectors.toList());
//asd.forEach(System.out::println);
//this outputs average
System.out.println(asd.stream().mapToDouble(val -> val).sum()/asd.size());
//this outputs sum
System.out.println(asd.stream().mapToInt(val -> val).sum());
//another way to achieve this thanks to commenter
System.out.println(IntStream.of(asd).summaryStatistics());