Question

我需要使用字符串，字符，一堆嵌套循环和条件语句为我的CS类构建此ISBN校验和生成器（对于ISBN-10和ISBN-13）。在混乱中的某个地方，我认为某些事情会触发无限循环，因为当系统提示我输入信息时，我给出输入并按Enter键，它会转到新的一行，并希望我输入更多的数据，而我猜测每次成功输入后，它应该提示我再次输入另一个，否则告诉我这是不正确的，然后再次要求另一次输入。而且，当我键入quit时，它并不会像预期的那样结束程序并显示校验和结果，而是表现出与其他输入相同的行为。如果我第一次输入quit而没有给程序提供任何数字，则它确实会正确结束程序，但是输出变量的值当然为null。

到目前为止，我的代码：

/******************************************************************************
 * Program Name:          Lab05A - ISBN
 * Program Description:   Calculate ISBN-10 AND ISBN-13
 * Program Author:        xxxxxxxxx
 * Date Created:          10/10/2018
 * Change#        Change Date      Programmer Name        Description
 * -------        ------------     -------------------    ---------------------
******************************************************************************/
package lab05a;
import java.util.Scanner;
public class Lab05A {
    public static void main(String[] args) {
        // Input for s
        Scanner input = new Scanner(System.in); // Create new scanner
        System.out.println("Enter the first 9 or 12 digits of an ISBN number. Enter QUIT to exit: "); // our ever-lasting prompt
        String s = input.next(); // declare string variable "s" and set it equal to next input from user.
        String output10 = null; // Declaring string output10
        String output13 = null; // Declaring string output13
        // main while loop
        while (!"QUIT".equals(s)) { //this will run as long as the program does not receive an input of "QUIT", not case sensitive.
            char checkDigit;
            char checkSum = '0';
            if (s.length() == 9) { //if the length of the inputted string is 9 characters...
                int sum = 0; // initialize sum variable
                for (int i=0; i <= s.length();) {
                    sum = sum + ((s.charAt(i) - '0') * (i + 1));
                }
                if (sum % 11 == 10) {
                    checkDigit = 'X';
                }
                else {
                    checkDigit = (char) ('0' + (sum % 11));
                }
                output10 = output10 + "\n" + s + checkDigit;
                System.out.println("Enter the first 9 or 12 digits of an ISBN number. Enter QUIT to exit: ");
                s = input.next();
            }
            else if  (s.length() == 12) {
               int sum = 0;
                for (int i=0; i <= s.length();) {
                    if (i % 2 == 0) {
                        sum = sum + (s.charAt(i) - '0');
                    }
                    else {
                        sum = sum + (s.charAt(i) - '0') * 3;
                    }
                    checkSum = (char) (10 - sum % 10);
                    if (checkSum == 10) {
                        checkSum = 0;
                    }
                    output13 = "\n" + output13 + checkSum;
                    System.out.println("Enter the first 9 or 12 digits of an ISBN number. Enter QUIT to exit: ");
                    s = input.next();
                }
            }
            else if (!s.toUpperCase().equals("QUIT")) {
                System.out.println(s + " is invalid input.");
                System.out.println("Enter the first 9 or 12 digits of an ISBN number. Enter QUIT to exit: ");
                s = input.next();
            }
        }
        System.out.println("The 10 digit ISBNs are \n" + output10);
        System.out.println("The 13 digit ISBNs are \n" + output13);
    }
}

Instructions

Flowchart as a separate image since it's kinda small in the instructions doc

感谢您的帮助。

Answer 1

是的，您在此for循环中缺少增量器

for (int i=0; i <= s.length();) {

更改为

for (int i=0; i <= s.length(); i++) {

我确定您不希望<=，也许只是<

如此

for (int i=0; i < s.length(); i++) {

顺便说一句，如果您调试代码，这很容易解决-这是一项基本技能-

修改

如果您具有以下代码（且s.length == 12）

for (int i=0; i < s.length(); i++) {
    System.out.println("Enter the first 9 or 12 digits of an ISBN number. Enter QUIT to exit: ");
    s = input.next();
}

然后它将执行12次。修正循环

Answer 2

更新代码，因为我在这里实施了一些建议：

package lab05a;
import java.util.Scanner;
public class Lab05A {
    public static void main(String[] args) {
        // Input for s
        Scanner input = new Scanner(System.in); // Create new scanner
        System.out.println("Enter the first 9 or 12 digits of an ISBN number. Enter QUIT to exit: "); // our ever-lasting prompt
        String s = input.next(); // declare string variable "s" and set it equal to next input from user.
        String output10 = ""; // Declaring string output10
        String output13 = ""; // Declaring string output13
        // main while loop
        while (!"QUIT".equalsIgnoreCase(s)) { //this will run as long as the program does not receive an input of "QUIT", not case sensitive.
            char checkDigit;
            char checkSum = '0';
            if (s.length() == 9) { //if the length of the inputted string is 9 characters...
                int sum = 0; // initialize sum variable
                for (int i=0; i < s.length(); i++) {
                    sum = sum + ((s.charAt(i) - '0') * (i + 1));
                }
                if (sum % 11 == 10) {
                    checkDigit = 'X';
                }
                else {
                    checkDigit = (char) ('0' + (sum % 11));
                }
                output10 = output10 + "\n" + s + checkDigit;
                System.out.println("Enter the first 9 or 12 digits of an ISBN number. Enter QUIT to exit: ");
                s = input.next();
            }
            else if  (s.length() == 12) {
               int sum = 0;
                for (int i=0; i < s.length(); i++) {
                    if (i % 2 == 0) {
                        sum = sum + (s.charAt(i) - '0');
                    }
                    else {
                        sum = sum + (s.charAt(i) - '0') * 3;
                    }
                    checkSum = (char) (10 - sum % 10);
                    if (checkSum == 10) {
                        checkSum = 0;
                    }
                    output13 = "\n" + output13 + s + checkSum;
                    System.out.println("Enter the first 9 or 12 digits of an ISBN number. Enter QUIT to exit: ");
                    s = input.next();
                }
            }
            else if (!"QUIT".equalsIgnoreCase(s)) {
                System.out.println(s + " is invalid input.");
                System.out.println("Enter the first 9 or 12 digits of an ISBN number. Enter QUIT to exit: ");
                s = input.next();
            }
        }
        System.out.println("The 10 digit ISBNs are \n" + output10);
        System.out.println("The 13 digit ISBNs are \n" + output13);
    }
}

Java ISBN校验和生成器-无限循环？

2 个答案: