c - 我从下面的程序中收到了我想要的错误消息，但我不知道为什么。（在 dev c++ 中使用 c 编程）

Question

下面的代码是我的 ICT 老师给我的作业。我的客人是因为当我输入错误的字母类时我的 if-else 语句运行了两次，但是，我不知道如何解决它。

#include <stdio.h>
#include <ctype.h>
int main ()
{
float rate, distance, claim; 
char class;

printf("......................................................\n");
printf("\t\t\t Class of Vehicle\n");
printf("......................................................\n");
printf("\t\t\t  A   B   C   D\n");
printf("\tRate  (cent/km)\t  70  60  50  45\n");    
printf("......................................................\n\n");

label1:
    printf("Enter Class of Vehicle\t\t: ");
    scanf("%c", &class);
    class = toupper(class);

if (class == 'A')
{
    rate = 70;
}
    else if (class == 'B')
    {
        rate = 60;
    }
        else if (class == 'C')
        {
            rate = 50;
        }
            else if (class == 'D')
            {
                rate = 45;
            }
                else
                {
                    printf("Invalid input. Please start again.\n");
                    goto label1;
                }

label2: 
printf("Enter Distance Travelled (km)\t: ");
scanf("%f", &distance);

if (distance < 0 )
{
    printf("Invalid input. Please start again.\n");
    goto label2;
}

claim = rate / 100 * distance;

printf("Amount of Claim (RM)\t\t: %.2f", claim);

return 0;
}

标签： cdev-c++