Question

我写了这段代码来确定两个数字之间哪些数字是某些类型是素数，哪些是复合数。用户键入两个数字，例如5＆amp; 10，在这种情况下程序应该输出：

5是素数 6不是素数 7是素数 8不是素数 9不是素数 10不是素数

但它没有正确地做到这一点。例如，如果用户输入13和33，则输出是13,14和15是素数，但所有其他数字都不是。更奇怪的是，结果相互矛盾。例如，如果用户输入10和20，则程序输出所有数字都不是素数。

package more.basic.applications;
import java.util.Scanner;

public class MoreBasicApplications {

public static void main(String[] args) 
{       

    //program to determine how many numbers between 2 numbers inclusive are prime, and how many are composite, as well as display them

    int j = 2;
    Scanner reader = new Scanner(System.in);
    System.out.println("Please enter number 1, between 0 and 100: ");
    int number = reader.nextInt(); 

    boolean composite = false;  

    System.out.println("Please enter number 2, between 0 and 200: ");
    int number2 = reader.nextInt();

    int difference = number2 - number; 

    int[] array = new int[difference+1]; 

    for (int i = 0; i < array.length; i++) 
    {
        array[i] = number + i; 

        while (j <= Math.sqrt(array[i])) 
        {        
            if (array[i]%j == 0) {
                composite = true; 
            }
            j++; 
        }

        if (composite == true) {
            System.out.println (array[i] + " is not prime.");
        }
        else 
        {        
            System.out.println (array[i] + " is prime.");
        }
    }
}

Answer 1

看起来你没有在j循环开始时将for“重置”回2，所以j会越来越大。

for (int i = 0; i < array.length; i++) {
  j = 2; // reset j back to 2.
  array[i] = number + i; 

  while (j <= Math.sqrt(array[i])) { 

    if (array[i]%j == 0) {
      composite = true; 
    }
    j++; 
  }
  if (composite == true) {
    System.out.println (array[i] + " is not prime.")
  } else {
    System.out.println (array[i] + " is prime.");
  }
 }

程序错误地指出数字是否为素数

1 个答案: