c - 程序跳过 switch case 中的所有 case 并转到 default

Question

我正在尝试构建一个使用用户输入的小程序，然后使用 switch case 执行适合用户输入的操作。我一直在努力寻找我的程序中的错误，但没有运气。显然我缺少一些东西。

这是代码，你能帮我看看它有什么问题吗？

#include <stdio.h>
#define A 8.5
#define B 7.6
#define C 7.7
#define D 7.7

int main ()
{


    char fuel;
    float amount,total;

    printf("please enter the desired fuel\n");
    scanf_s("%c",&fuel);

   switch(fuel)
   {
   case 'A' :
         printf("how many liters of fuel do you want?\n");
         scanf_s("%f",&amount);
         total=amount*A;
         if(total>150)
         {
             printf("the total price to pay is %.3f: \nYou have won a newspaper", total);
         }
         else
         printf("the total price to pay is %.3f", total);
         break;

      case 'B' :
          printf("how many liters of fuel do you want?\n");
         scanf_s("%f",&amount);
         total=amount*B;
         if(total>150)
             printf("the total price to pay is %f: \nYou have won a newspaper", total);
         else
         printf("the total price to pay is %.3f", total);

          break;
      case 'C' :
         printf("how many liters of fuel do you want?\n");
         scanf_s("%f",&amount);
         total=amount*C;
         if(total>150)
             printf("the total price to pay is %f: \nYou have won a newspaper", total);
         else
         printf("the total price to pay is %.3f", total);
         break;

      case 'D' :
         printf("how many liters of fuel do you want?\n");
         scanf_s("%f",&amount);
         total=amount*D;
         if(total>150)
             printf("the total price to pay is %f: \nYou have won a newspaper", total);
         else
         printf("the total price to pay is %f", total);

      break;

      default: 
      printf("no\n");
      break;
   }



}

即使我输入“A”、“B”、“C”或“D”，它也会使用默认值，而不是适当的大小写。感谢您的帮助。

Answer 1

您没有正确使用scanf_s 函数。根据其documentation :

Unlike scanf and wscanf, scanf_s and wscanf_s require the buffer size to be specified for all input parameters of type c, C, s, S, or string control sets that are enclosed in []. The buffer size in characters is passed as an additional parameter immediately following the pointer to the buffer or variable.

并且还应该检查错误，所以你应该这样做:

char fuel;
if (scanf_s("%c", &fuel, 1) != 1)  {
    puts("Error from scanf_s");
    return 1;
}