计算质数(新手)

Question

这个程序检查用户输入的数字是否为质数。

我的问题出在if语句中。由于某些原因，Boolean从未被切换过。如果这个数是质数，它只会给出两个结果。

我遗漏了什么？

import java.util.Scanner;
public class Prime 
{

     public static void main(String[] args)
    {
       System.out.println("Enter a number to check if it is prime:");
       Scanner kb = new Scanner(System.in);
       int n = kb.nextInt();
       boolean more = true;

       do
       {
           for (int i = 2; i <= n; i++)
           {
               if (n <=1 || n%i==0) 
               {
                    System.out.println(n + " is not prime");
                    more = false;
               }              
            } 
       }
       while (more);
       System.out.println(n + " is prime");
    }
}

Answer 1

删除if()中的打印代码，并在do while循环之后使用以下代码

if(more)
 System.out.println(n + " is prime");
else
 System.out.println(n + " is not prime");

而且你也不需要一个do while循环删除it.Complete代码

 System.out.println("Enter a number to check if it is prime:");
 Scanner kb = new Scanner(System. in );
 int n = kb.nextInt();
 boolean more = true;


 for (int i = 2; i <= n / 2; i++) {
    if (n <= 1 || n % i == 0) {

        more = false;
        break;
    }
 }
 if (more) System.out.println(n + " is prime");
 else System.out.println(n + " is not prime");

Answer 2

使用for循环可以在几行代码中检查质数。这对性能更好。

用于检查素数的代码：

    boolean isPrime = true;
    for (int i = 2; i < n && isPrime; i++) {
        isPrime = !(n % i == 0);
    }

根据您的示例完整类：

import java.util.Scanner;

public class Prime {

    public static void main(String[] args) {
        System.out.println("Enter a number to check if it is prime:");
        Scanner kb = new Scanner(System.in);
        int n = kb.nextInt();

        boolean isPrime = true;
        for (int i = 2; i < n && isPrime; i++) {
            isPrime = !(n % i == 0);
        }

        System.out.println(n + " is prime - " + isPrime);
    }
}

Answer 3

试试这个：

public static void main(String[] args) {
        System.out.println("Enter a number to check if it is prime:");
           Scanner kb = new Scanner(System.in);
           int n = kb.nextInt();
           boolean prime = true;

               for (int i = 2; i <n; i++)
               {
                   if (n <=1 || n%i==0) 
                   {
                        prime = false;
                        break;
                   }
                }
               if(prime)
               {
                   System.out.println(n + " is prime");
               }
               else
               {
                   System.out.println("Not prime");
               }
    }