java - 用用户输入填充数组并使用 if 语句根据数组内的值进行算术运算

Question

问题是:

编写一个Java程序，读取一系列正整数，并写出所有小于25的整数与所有大于或等于25的整数之和的乘积。使用0作为标记值。

我能够理解如何让用户将输入添加到数组中。但我找不到一种方法将代码与 if 语句集成以生成完整的工作程序来完成该任务。这是我目前的发现；

import java.util.*;
public class UserInput {
    public static void main(String[] args) {

        List<String> list = new ArrayList<String>();
        Scanner stdin = new Scanner(System.in);

        do {
            System.out.println("Current list is " + list);
            System.out.println("Add more? (y/n)");
            if (stdin.next().startsWith("y")) {
                System.out.println("Enter : ");
                list.add(stdin.next());
            } else {
                break;
            }
        } while (true);

        System.out.println("List is " + list);
        String[] arr = list.toArray(new String[0]);
        System.out.println("Array is " + Arrays.toString(arr));
    }
}

如何让数组读取输入并找到 25 以下所有数字与 25 以上所有数字之和的乘积。在这之间，什么是哨兵值以及知道它有什么用处？

解决方案:经过几个小时的调整下面志愿者发布的答案，我找到了一个适合我的解决方案。我特此发布，以防有​​人觉得有用；

import java.util.*;
  public class UserInput {
  public static void main(String[] args) {

List<Integer> list = new ArrayList<Integer>();
Scanner stdin = new Scanner(System.in);
do{
    System.out.println("Current list is : " + list);
    System.out.println("Enter number : ");
    int  entered = stdin.nextInt();
    if(entered == 0){
        int sum = 0,product = 1;
        for(Integer number : list){
            if(number<25){
                sum += number; 
            }else if(number >= 25){
                product *= number;
            }
        }
        System.out.println("sum : " + sum);
        System.out.println("product : " + product);
    }else{
        list.add(entered);
        int sum = 0,product = 1;
        for(Integer number : list){
            if(number<25){
                sum += number; 
            }else if(number >= 25){
                product *= number;
            }
        }
        System.out.println("sum : " + sum);
        System.out.println("product : " + product);
    }           
    System.out.println("Add more numbers to the list ? (Y/N) : ");

    } while(stdin.next().equalsIgnoreCase("y"));
}
}

感谢大家的发帖和评论!这真的很有帮助! :)

Answer 1

Class Main {

    public static void main(String[] args) {

        List<Integer> numsGe25 = new ArrayList<>();  // Store numbers greather than or equal to 25 

        List<Integer> numsLt25 = new ArrayList<>();  // Store numbers less than 25


        Scanner in = new Scanner(System.in);
        int num = -1;
        // Reads a number from the standard input till the 0 value is inserted. 0 is the sentinel
        while ((num = in.nextInt()) != 0) {  
            if (num >= 25) {
                numsGe25.add(num)   
            } else {
                numsLt25.add(num);
            }
        }
        System.out.println("sum of numbers >= 25: " + sum(numsGe25));
        System.out.println("product of numbers < 25: " + product(numsLt25));
    }

    private static int sum(List<Integer> numbers) {
        int result = 0;
        for (Integer num : numbers) {
            result += num;
        }
        return result; 
    }

    private static int product(List<Integer> numbers) {
        int result = 1;
        for (Integer num : numbers) {
            result *= num;
        }
        return result;
    }
}