Question

我正在创建一个程序，它打印从0到用户输入数字的偶数之和。例如，如果用户输入数字20，程序将计算0到20之间所有偶数的总和。

当我使用数字10测试程序时，它有效。但我尝试使用不同的数字，35，它只是陷入无限循环。我将不胜感激任何帮助。代码将发布在下面：

（编辑）感谢大家的反馈！在与朋友交谈后，我们意识到解决方案实际上非常简单。我们只是让它变得复杂。不过，感谢所有的建议。

//**************************************************************
 // Prints the sum of the even numbers within a range of 0
 // and the integer that the user enters.
 //
 // @me
 // @version_1.0_11.7.17
 //**************************************************************
 import java.util.Scanner;

public class EvenNumbersSum
{
    public static void main(String[] args)
    {
        Scanner input = new Scanner(System.in);
        int user_num = 2;   // variable that stores the user's number
        int sum;    // stores the sum of the needed values

        System.out.print("Enter an integer greater than or equal to, 2: "); // prompt user for input
        user_num = input.nextInt();

        // checks to see if the value entered is valid or not.
        while (user_num < 2)
        {
            System.out.println("Invalid entry. Must enter an integer greater than or equal to, 2.\n");
            System.out.print("Enter an integer greater than or equal to, 2: ");
            user_num = input.nextInt();
        }

        // starts adding the values
        for (sum = 0; sum <= user_num;)
        {
            if (user_num % 2 == 0)  // checks if the number is even
                sum+=user_num;  // add the number to sum
            else
                continue;  // I thought that I might need this, but ended up changing nothing.
        }

        System.out.println();   // extra line for cleanliness
        System.out.printf("The sum of the even numbers between 0 and %d is %d.", user_num, sum);    // prints the result
    }
}

Answer 1

为什么要为此编写循环，有效的方法。

Sum of numbers between 1-N = (N(N+1))/2

Sum of even numbers between 1-N = (N(N+2))/4

其中N =用户给定的输入数，您希望添加偶数

注意：您可以在输入数字上添加验证，即使是（n％2 == 0），如果不是

则返回错误

Answer 2

你在条件中使用的变量（即 sum ＆amp; user_num ）在奇数的情况下没有人改变，你的代码卡在永无止境的循环中。您应该使用计数器变量（例如 i 从1到user_num）并在条件中使用该数字。例如：

    // starts adding the values
    sum = 0;
    for (int i = 0; i <= user_num; i++)
    {
        if (i % 2 == 0)  // checks if the number is even
            sum+=i;  // add the number to sum
    }

Answer 3

你的for循环应该是这样的。

int total_sum = 0; 
for (int sum = 0; sum <= user_num; sum++)
        {
            if (sum % 2 == 0)  // checks if the number is even
                total_sum+=sum;  // add the number to total sum
            else
                continue;  // I thought that I might need this, but ended up changing nothing.
        }
// note print total sum
System.out.println(totalsum);

你的初始程序只是检查输入的数字是偶数还是奇数。和输入的数字相加。因此总和是输入数字的两倍是偶数。如果输入的数字是奇数，它将进入无限循环，因为entered_num（奇数）％2 == 0总是为false并执行else语句。

Java程序无限循环，偶数整数

3 个答案: