Java回文项目: If/else

Question

我正在为一个项目编写一个Java程序，用于查找3位数字是否是回文数，当我完成它时，我没有意识到指令还说它必须检测它是否是回文数是否是 3 位数字，我不知道如何将其实现到我所拥有的中。

我不能使用数组或循环，因为我们没有在类里面讨论它们，而且我的教授不希望我们使用任何我们在技术上不应该知道的东西。必须通过所有输入和数学才能找到数字。

代码可以工作，但我的问题出在 ints d1、d2 和 d3 启动的区域。我想我需要将“if (d1 == d3)”嵌套在另一个 if 语句中来确定数字是否为 3 位数字。在过去的几天里，我尝试自己解决这个问题，但我陷入了困境。

感谢任何帮助，谢谢。

import java.util.Scanner;
import java.lang.Math;

public class Palindrome {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        //user or computer generated number
        System.out.print("Enter 1 if you would like to enter a 3-digit number. Enter 2 if you would like to have the computer generate it. ");
        int firstChoice = input.nextInt();

        //user entered number
        if (firstChoice == 1) {

            //enter the 3 digit number
            System.out.print("Enter a 3-digit number: ");
            int userNumbers = input.nextInt();

            //3 user numbers
            int d1 = userNumbers / 100;
            int d2 = (userNumbers / 100) / 10;
            int d3 = userNumbers % 10;


            if (d1 == d3) {
                System.out.println(userNumbers + " is a palindrome");
            } else {
                System.out.print(userNumbers + " is not a palindrome");
            }

            //computer generated number
        } else if (firstChoice == 2) {

            int low = 0;
            int high = 10;

            //generate 3 random numbers
            int num1 = (int)(Math.random() * ((high - low) - 1) + low);
            int num2 = (int)(Math.random() * ((high - low) - 1) + low);
            int num3 = (int)(Math.random() * ((high - low) - 1) + low);

            //computer number is or isn't a palindrome
            if (num1 == num3) {
                System.out.println(num1 + "" + num2 + "" + num3 + "");
                System.out.print(num1 + "" + num2 + "" + num3 + " is a palindrome");
            } else {
                System.out.println(num1 + "" + num2 + "" + num3 + "");
                System.out.print(num1 + "" + num2 + "" + num3 + " is not a palindrome");
            }
            //incorrect input
        } else {
            System.out.println("Incorrect input");
        }
    }
}

Answer 1

按如下方式进行:

// user entered number  
if (firstChoice == 1) {
    int userNumbers;
    // enter the 3 digit number
    do {
        System.out.print("Enter a 3-digit number: ");
        userNumbers = input.nextInt();
        if (userNumbers >= 100 && userNumbers <= 999) {
            // 3 user numbers
            int d1 = userNumbers / 100;
            int d3 = userNumbers % 10;

            if (d1 == d3) {
                System.out.println(userNumbers + " is a palindrome");
            } else {
                System.out.print(userNumbers + " is not a palindrome");
            }
        } else {
            System.out.println("The number has to be of 3 digits");
        }
    } while (!(userNumbers >= 100 && userNumbers <= 999));

    // computer generated number
} else if (firstChoice == 2) {
    // ...
}

示例运行:

Enter 1 if you would like to enter a 3-digit number. Enter 2 if you would like to have the computer generate it. 1
Enter a 3-digit number: 12
The number has to be of 3 digits
Enter a 3-digit number: 2000
The number has to be of 3 digits
Enter a 3-digit number: 121
121 is a palindrome

另一个示例运行:

Enter 1 if you would like to enter a 3-digit number. Enter 2 if you would like to have the computer generate it. 1
Enter a 3-digit number: 123
123 is not a palindrome

您还可以重写逻辑来检查计算机生成的 3 位随机数，如下所示:

if (firstChoice == 1) {// user entered number
    int userNumbers;
    // enter the 3 digit number
    do {
        System.out.print("Enter a 3-digit number: ");
        userNumbers = input.nextInt();
        if (userNumbers >= 100 && userNumbers <= 999) {
            // 3 user numbers
            int d1 = userNumbers / 100;
            int d3 = userNumbers % 10;

            if (d1 == d3) {
                System.out.println(userNumbers + " is a palindrome");
            } else {
                System.out.print(userNumbers + " is not a palindrome");
            }
        } else {
            System.out.println("The number has to be of 3 digits");
        }
    } while (!(userNumbers >= 100 && userNumbers <= 999));  
} else if (firstChoice == 2) {// computer generated number    
    int low = 0;
    int high = 1000;    
    // generate a 3-digit random number
    int num = (int) (Math.random() * ((high - low) - 1) + low);    
    int d1 = num / 100;
    int d3 = num % 10;    

    if (d1 == d3) {
        System.out.println(num + " is a palindrome");
    } else {
        System.out.print(num + " is not a palindrome");
    }
}

如有任何疑问，请随时发表评论。