Question

我需要将数值转换为罗马数字，而且我遇到了一些麻烦。当我测试我的代码并且用户输入一个数字时，代码会将其转换为罗马数字，但我无法在之后再次显示提示;放置一个不正确的整数后它会重新设置好，但是在正确的整数之后不能。我不知道如何制作它以便用户可以继续转换值，直到他们选择-1退出。以下是我迄今为止所提出的建议。

import java.util.Scanner;

public class arabicToRoman {
static String a = "";

public static void main (String[] args){

    Scanner input = new Scanner(System.in);
    System.out.println("Enter a number between 1 and 3999 (-1 to quit): ");

    while (!input.hasNext("-1")) {
        String a = input.next(); 

    try {
        Integer number = Integer.parseInt(a); 

        if ((number <= 3999) && (number > 0)) {
            System.out.println(arabicToRoman(number)); 

        } else if (number > 3999) {
            System.out.println("Error: number must be between 1 and 3999");

        } else if (number == 0) {
            System.out.println("Error: The Romans did not have a way to represent negative numbers or zero.");

        } else {
            System.out.println("Error: The Romans did not have a way to represent negative numbers or zero.");

        }
    } catch (NumberFormatException e) {
        System.out.println("You did not enter a number!");
    }
}  
}

public static String arabicToRoman(int arabic) {    
    while (arabic >= 1000){
        a += "M";
        arabic -= 1000;
    }
    while (arabic >= 900){
        a += "CM";
        arabic -= 900;
    }
    while (arabic >= 500){
        a += "D";
        arabic -= 500;
    }
    while (arabic >= 400){
        a += "CD";
        arabic -= 400;
    }
    while (arabic >= 100){
        a += "C";
        arabic -= 100;
    }
    while (arabic >= 90){
        a += "XC";
        arabic -= 90;
    }
    while (arabic >= 50){
        a += "L";
        arabic -= 50;
    }
    while (arabic >= 40){
        a += "XL";
        arabic -= 40;
    }
    while (arabic >= 10){
        a += "X";
        arabic -= 10;
    }
    while (arabic >= 9){
        a += "IX";
        arabic -= 10;
    }
    while (arabic >= 5){
        a += "V";
        arabic -= 5;
    }
    while (arabic >= 4){
        a += "IV";
        arabic -= 4;
        }
    while (arabic >= 1){
        a += "I";
        arabic -= 1;
    }
    return a;
}
}

输入输入后，似乎显示结果，但之后没有提示，但是用户可以输入其他内容并将其读取;如果它是另一个数字，但结果会被添加到之前的结果中。

Answer 1

由于满足return条件时调用的((number <= 3999) && (number > 0))语句，您的代码无法正常运行。这个return终止循环。

相反，您可能希望调用方法arabicToRoman(int arabic)并简单地打印出结果。

我还会考虑重构您的代码，以便在sentinel value循环条件中使用while并编辑代码，以便在给出非数字答案时不会崩溃。由于您的代码现在已经编写，因此执行此操作会生成java.util.InputMismatchException。

Scanner input = new Scanner(System.in);
System.out.println("Enter a number between 1 and 3999 (-1 to quit):");

while (!input.hasNext("-1")) {

    String a = input.next(); // gets the next item from the Scanner

    try {
        Integer number = Integer.parseInt(a); // tries to 'cast' the String to an Integer

        if ((number <= 3999) && (number > 0)) {
            System.out.println(arabicToRoman(number)); // prints out the result

        } else if (number > 3999) {
            System.out.println("Error: number must be between 1 and 3999");

        } else if (number == 0) {
            System.out.println("Error: The Romans did not have a way to represent negative numbers or zero.");

        } else {
            System.out.println("Error: The Romans did not have a way to represent negative numbers or zero.");

        }
    } catch (NumberFormatException e) {
        System.out.println("You did not enter a number!");
    }
}

修改：修复连接问题

编写的程序将结果存储在state variable中，该a通过调用持久存储。这就是为什么每次调用该方法时，它都会打印附加到前一个结果的当前结果。您希望编辑代码以不将arabicToRoman(int arabic)存储为状态变量，并返回static String a = "";方法而不改变现有数据。声明方法内部的变量将允许在方法终止时将其处理掉。

要进行此修复：

首先，在类的方法之外删除此行：

arabicToRoman(int arabic)

然后，修改您的public static String arabicToRoman(int arabic) { String a = ""; // note this String declaration at the start of the method while (arabic >= 1000) { a += "M"; arabic -= 1000; } while (arabic >= 900) { a += "CM"; arabic -= 900; } while (arabic >= 500) { a += "D"; arabic -= 500; } while (arabic >= 400) { a += "CD"; arabic -= 400; } while (arabic >= 100) { a += "C"; arabic -= 100; } while (arabic >= 90) { a += "XC"; arabic -= 90; } while (arabic >= 50) { a += "L"; arabic -= 50; } while (arabic >= 40) { a += "XL"; arabic -= 40; } while (arabic >= 10) { a += "X"; arabic -= 10; } while (arabic >= 9) { a += "IX"; arabic -= 10; } while (arabic >= 5) { a += "V"; arabic -= 5; } while (arabic >= 4) { a += "IV"; arabic -= 4; } while (arabic >= 1) { a += "I"; arabic -= 1; } return a; }方法，使其如下所示：

{{1}}

我再次对此进行了测试，并确认它会产生与您描述的相同的正确行为。

为了清楚起见，this is what the final product should look like。

如何重新启用以允许用户继续转换值？

1 个答案: