Question

我对java很新。我有一个代码，其中一个用户输入一个数字，程序检查从1到n的每个数字，并输出每个数字，它们都是素数和回文。但是我的代码由于某种原因没有输出任何内容。代码中没有错误，所以我不确定究竟是什么错误。这是我的代码：

import java.util.*;
public class Lab5 
{
    public static void main (String[] args)  {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter a value:");  //Asking the user to input     the value n
        int n =scanner.nextInt();
        for (int y=2; y<=n; y++) { //For every number from 2 to n
            prime(y);                     //the prime number is checked
            pal(y);                         //and so is the palindrome
            if ((prime(y)==true) && (pal(y)==true)) { //if a number is both a prime AND a palindrome (both methods are being compared here)
                System.out.println(y);                          //it is printed out
            }
    }
    }
    public static boolean prime(int n) { //the method for finding the prime number
        int x = 2;
        while (n%x>0) {
        x+=1;
        } if (x==n) {
            return true;
    } else {
            return false;
        }
    }

public static boolean pal(int n) { //the method for finding a palindrome
    int rev = 0;
    int rmd = 0;
    while (n>0) {
        rmd = n%10;
        rev = rev*10 + rmd;
        n = n/10;
    } if (rev==n) {
        return true;
    } else {
        return false;
    }
}

}

Answer 1

你的回文方法返回了错误的结果。您正在修改n，然后与反转数字进行比较。

首先保存该值，然后在while循环

之后进行比较

int number = n;
If(rev == number)  return true;

Answer 2

您在pal()函数中犯了错误。你的n变量为0，你将它与反向编号进行比较。

将该变量分配给temp变量然后进行比较。我对您的代码进行了一些更改，它运行良好。

import java.util.*;
public class A 
{
    public static void main (String[] args)  {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter a value:");  //Asking the user to input     the value n
        int n =scanner.nextInt();
        for(int i=2;i<=n;i++){
            if (prime(i) && pal(i)) { //if a number is both a prime AND a palindrome (both methods are being compared here)
                System.out.println(i);                          //it is printed out
            }
        }
    }
    public static boolean prime(int n) { //the method for finding the prime number
        int x = 2;
        while (n%x>0) {
            x+=1;
        } if (x==n) {
            return true;
        } else {
            return false;
        }
    }
    public static boolean pal(int n) { //the method for finding a palindrome
        int rev = 0;
            int rmd = 0;
        int temp = n;
            while (n>0) {
                rmd = n%10;
                rev = rev*10 + rmd;
                n = n/10;
            }
        if (rev==temp){
                return true;
            }else{
                return false;
            }
    }
}

输出

找到一个既是素数又是回文数的数字

2 个答案: