Question

以下是用于将输入的卡号的数字相加的代码：

import java.util.Scanner;
import java.lang.*;
import java.math.*;
public class Assignment4
{
    public static void main(String[] args)
    {
        // introduce program
        System.out.println("\n========================");
        System.out.println("Card Number Verification");
        System.out.println("========================\n");

        Scanner sc = new Scanner(System.in); // initialize scanner

        // intialize any relevant variables
        String card_type = "0"; // for Visa or MasterCard in part 1
        int sum = 0; // sum for all digits in card number in part 2
        int num_check; // for modulo 10 of summation of digits in part 3

        /* Part 1: Determine users card type */

        System.out.println("Menu (choose number):");
        System.out.println("---------------------");
        System.out.println("1 - MasterCard");
        System.out.println("2 - Visa\n");

        int menu_choice = sc.nextInt();
        sc.nextLine();
        switch (menu_choice) {
        case 1:
            card_type = "MasterCard";
            break;
        case 2:
            card_type = "Visa";
            break;
        default:
            System.out.print("Not a menu option. Restart the program ");
            System.out.println("and choose 1 or 2.\n");
            System.exit(0);
        }

        /* Part 2: Obtain users card number and sum digits */

        System.out.print("\nEnter 16 digit card number (spaces every ");
        System.out.println("4 digits): ");
        String card_string = sc.nextLine(); //obtain users card number
        int length = card_string.length(); // get length of number

        // verify that it is 16 numeric characters.  '\\d{$} ' verifies
        if (card_string.matches("(\\d{4} \\d{4} \\d{4} \\d{4}") == false) { 
            System.out.print("\nNot a valid card number. Restart the program ");
            System.out.println("and enter a 16 digit number.\n");
            System.exit(0);
        }
        for (int i=0; i < length;) {
            // the following sum adds the value of the digit at point i
            if (i == 4 || i == 8 || i == 12) {
                i++;
                else {
                    sum += Character.getNumericValue(card_string.charAt(i));
                    i++;
                    //System.out.println(sum); // used for testing
                }
            }

            /* Part 3: Check validity of users card number */

            num_check = sum % 10; // modulo 10 of summation of digits
            if (card_type == "MasterCard") {
                if (num_check == 1) {
                    System.out.println("\nValid MasterCard number!\n");
                }
                else {
                    System.out.println("\nInvalid MasterCard number.\n");
                }
            }
            else {
                if (num_check == 0) {
                    System.out.println("\nValid Visa card number!\n");
                }
                else {
                    System.out.println("\nInvalid Visa card number!\n");
                }
            }
            System.exit(0);
        }
    }

这是它产生的错误：

Assignment4.java:60: 'else' without 'if'
            else {
            ^
Assignment4.java:88: reached end of file while parsing
}
 ^
2 errors
Jordans-MacBook-Pro:CSE_110_hw JPagz95$ javac Assignment4.java 
Assignment4.java:59: 'else' without 'if'
            else {
            ^
Assignment4.java:87: reached end of file while parsing
}
 ^
2 errors

有人可以解释为什么它不承认我有if语句？当我更改if语句以识别何时i是某个值（4,8,12不求和）时，问题就开始了。一切都有帮助。我会在一两个小时（晚餐时间）给出最佳答案：）

Answer 1

您的if / else定位错误。应该是

if (i == 4 || i == 8 || i == 12) { 
    i++;
} 
else {
    sum += Character.getNumericValue(card_string.charAt(i));
    i++;
    //System.out.println(sum); // used for testing
}

Answer 2

你的if块只是错过了它的结束括号：）

  if (i == 4 || i == 8 || i == 12) {
            i++;
  }
   else {
         sum += Character.getNumericValue(card_string.charAt(i));
         i++;
         //System.out.println(sum); // used for testing
    }

说我没有if声明，但我明确表示吗？

2 个答案: