Question

我正在使用switch语句创建此程序，该语句将根据用户是否输入数字0-10来指定字母等级。如果用户输入的数字不是0-10，程序将输出错误消息并具有用户重新进入。但是，如果用户输入一个字符，程序将以默认情况循环。我希望它从默认情况下输出一次错误消息，并让它们在输入字符时重新输入。我不确定为什么它会在输入字符时循环默认情况。

#include <stdio.h>

int main()
{
    int grade;
    int r;
    while((r = scanf("%i", &grade)) != EOF)
    {
        switch(grade)
            {
                case 10:
                case 9:
                    printf("Your grade is an A\n");
                    break;
                case 8:
                    printf("Your grade is a B\n");
                    break;
                case 7:
                    printf("Your grade is a C\n");
                    break;
                case 6:
                    printf("Your grade is a D\n");
                    break;
                case 5:
                case 4:
                case 3:
                case 2:
                case 1:
                case 0:
                    printf("Your grade is an F\n");
                    break;
                default:
                    printf("Invalid score, please re-enter\n");
            }
    }

    return 0;
}

Answer 1

尝试类似：

    func frameForBarButton(btn: UIBarButtonItem) -> CGRect {
        let view: UIView = btn.valueForKey("view") as! UIView
        return view.frame
    }

Answer 2

这将清除无效输入上的输入缓冲区并允许重试。

#include <stdio.h>

int main()
{
    int grade;
    int r;
    while((r = scanf("%i", &grade)) != EOF)
    {
        if ( r != 1) {//r == 1 is successful input of integer
            grade = -1;//reset grade on invalid input
        }
        switch(grade)
        {
            case 10:
            case 9:
                printf("Your grade is an A\n");
                break;
            case 8:
                printf("Your grade is a B\n");
                break;
            case 7:
                printf("Your grade is a C\n");
                break;
            case 6:
                printf("Your grade is a D\n");
                break;
            case 5:
            case 4:
            case 3:
            case 2:
            case 1:
            case 0:
                printf("Your grade is an F\n");
                break;
            default:
                printf("Invalid score, please re-enter\n");
                while ( getchar() != '\n');//clear input buffer
        }
    }
    return 0;
}

Answer 3

你的代码总是循环的原因是因为除了杀死程序之外没有办法退出break。请注意，switch只会突破最内层的bool valid_grade = false; while(!valid_grade && (r = scanf("%i", &grade)) != EOF) { valid_grade = true; switch(grade) { case 10: // unchanged from your code default: valid_grade = false; printf("Invalid score, please re-enter\n"); } }或循环。

打破多个级别的最简洁方法是使用标志。做你想做的事的一种方法是：

Select  Application_Number  
       ,Id_Number1  
       ,'Alias'  + CAST( ROW_NUMBER() 
                         OVER (ORDER BY Application_Number) AS Varchar) AS Name
FROM Table Name

为什么我的程序不会标记字符？

3 个答案: