Question

错误：

CreditCard.java:180: error: cannot find symbol
        } while (cardNum7 != 0);
                 ^
  symbol:   variable cardNum7
  location: class CreditCard
1 error
Process javac exited with code 1

代码：

do {
    //Declarations
    long cardNum7 = 0;
    //testing
    System.out.print("Enter a card number (type 0 to end program): ");
    cardNum7 = keyboard.nextLong();
    System.out.println("Your credit card is " + isValid(cardNum7));
} while (cardNum7 != 0);

Answer 1

cardNum7在do-while块中声明。它不存在于特定代码块之外，因此您无法在此处访问它：

} while (cardNum7 != 0);

您可以在do-while之前声明cardNum7，以使其可以访问while语句。

Answer 2

您在循环内声明了cardNum7，因此它不会在循环外反映出来。使用：

//Declarations
long cardNum7 = 0;
do {
    //testing
    System.out.print("Enter a card number (type 0 to end program): ");
    cardNum7 = keyboard.nextLong();
    System.out.println("Your credit card is " + isValid(cardNum7));
} while (cardNum7 != 0);

为什么我一直在为丢失的符号收到编译错误？

2 个答案: