Question

我在完成这个程序时遇到了麻烦。我理解该程序应该做什么，但我在完成它时遇到了麻烦。我的代码发布在下面。

对于这个程序，我需要确定一个数字是否是素数。从这个角度来看，我需要让用户输入一个范围（例如1-10）并显示哪些数字是素数而哪些不是。

这就是我到目前为止......

import java.util.Scanner;
public class PrimeNumbers
{
    public static void main(String[]args)
    {
        //Create Scanner Object
        Scanner input = new Scanner(System.in);

        //Initialize variable 
        double num1, range;


        //Prompt the user to enter in a number
        do
        {
            System.out.println("Please enter in a number:");
            num1 = input.nextDouble();

            //Decision making
            if(num1 % 2 == 0 || num1 % 3 == 0 || num1 % 4 == 0 || num1 % 5 == 0 || num1 % 6 == 0 || num1 % 7 ==0 || num1 % 8 ==0 || num1 % 9 == 0)
            {
                //Display message
                System.out.println(num1 + " is not a prime number.");

                System.out.println("Please enter a range: ");
                range = input.nextInt();

                if ()
            }

            else
                //Display output
                System.out.println(num1 + " is prime.");

        }

        while(num1 == -1);
        {
            System.out.println("This program has now ended.");
        }

    }
}

Answer 1

http://beginnersbook.com/2014/01/java-program-to-display-prime-numbers/

import java.util.Scanner;
class PrimeNumbers2
{
   public static void main (String[] args)
   {        
      Scanner scanner = new Scanner(System.in);
      int i =0;
      int num =0;
      //Empty String
      String  primeNumbers = "";
      System.out.println("Enter the value of n:");
      int n = scanner.nextInt();
      for (i = 1; i <= n; i++)         
      {                   
         int counter=0;           
         for(num =i; num>=1; num--)
         {
        if(i%num==0)
        {
        counter = counter + 1;
        }
     }
     if (counter ==2)
     {
        //Appended the Prime number to the String
        primeNumbers = primeNumbers + i + " ";
     }  
      } 
      System.out.println("Prime numbers from 1 to n are :");
      System.out.println(primeNumbers);
   }
}

Answer 2

这里是显示特定范围内的素数的代码，

import java.util.Scanner;

public class JavaPrograms 
{
   public static void main(String[] args) 
   {
      Scanner sc = new Scanner(System.in); 
      System.out.print("Please enter the first number : "); 
      int start = sc.nextInt(); 
      System.out.print("Please enter the second number : "); 
      int end = sc.nextInt(); 
      System.out.println("List of prime number in java between " + start + " and " + end + " : "); 
      for(int a = start; a <= end; a++) 
      { 
         if(checkPrime(a)) 
         { 
            System.out.println(a); 
         } 
      }
      sc.close();
   }

   public static boolean checkPrime(int number) 
   { 
      if(number <= 1) 
      { 
         return false; 
      } 
      for(int a = 2; a <= Math.sqrt(number); a++) 
      { 
         if(number % a == 0) 
         { 
            return false; 
         } 
      } 
      return true; 
   } 
}

有关素数java程序的更多信息，请参阅this资源。

如何使用while循环完成此程序的编写？

2 个答案: