Question

===== CS302 TOOL BOX =====
T > COIN TOSS SIMULATOR
G > GRADE ESTIMATOR
C > COLOR CHALLENGE
Q > QUIT
Type code letter for your choices: h
Invalid selection. Please try agian: 
t
Invalid selection. Please try agian: 
T

^这是我在运行程序时给出的错误猜测。循环用于验证用户输入，因此它完全失败。关于我做错了什么的任何想法？谢谢你的时间！

}

    System.out.println("===== CS302 TOOL BOX =====");
    System.out.println("T > COIN TOSS SIMULATOR");
    System.out.println("G > GRADE ESTIMATOR");
    System.out.println("C > COLOR CHALLENGE");
    System.out.println("Q > QUIT");
    System.out.print("Type code letter for your choices: ");
    boolean code_letter;
    String code_choice = scanner.next();
    do {
        if (code_choice.toUpperCase().equals("Q")
                || (code_choice.toUpperCase()).equals("C")
                || (code_choice.toUpperCase()).equals("G")
                || (code_choice.toUpperCase()).equals("T")) {
            code_letter = true;
        }

        else {
            System.out.println("Invalid selection. Please try agian: ");
            code_letter = false;
            scanner.next();
        }
    } while (!(code_letter));

    {

        System.out.println("you did it?");
    }

}
}

Answer 1

初始化code_choice循环中的do-while变量，否则变量将不会在条件测试之前的循环的每次迭代中重新初始化。

String code_choice = scanner.next();

像这样

//declared it outside to take care of the scope
String code_choice = null;
    do {
        //initialize it every time before you perform the conditional test.
        //This increases the readability!
        code_choice = scanner.next();
        if (code_choice.toUpperCase().equals("Q")
                || (code_choice.toUpperCase()).equals("C")
                || (code_choice.toUpperCase()).equals("G")
                || (code_choice.toUpperCase()).equals("T")) {
            code_letter = true;
        }

        else {
            System.out.println("Invalid selection. Please try agian: ");
            code_letter = false;
        }
    } while (!(code_letter));

希望这有帮助！

Answer 2

试试..

把你的

scanner.next()

在if之前的

，删除

周围的花括号

System.out.println("you did it?");

最后你的......改变它......

while(code_letter !=  true);

Answer 3

我假设扫描仪（小写S）是扫描仪对象？请在下次包含所有相关代码，否则调试问题非常困难。

你遇到的主要问题是在else条件下的行。 scanner.next（）不做任何事情。你需要这样做：

else {
    System.out.println("Invalid selection. Please try agian: ");
    code_letter = false;
    code_choice = scanner.next(); // This needs to be modified
}

这应该让它发挥作用。

输入验证（do-while循环）出现故障

3 个答案: