无论如何，Switch 语句都会使用默认大小写 - C 初学者

Question

//此代码应该添加或减去并跟踪四个具有个人 ID 的不同啤酒品牌。使用 -1 会退出，但使用 ID 号 1-4 中的任何一个都会导致程序执行默认情况。

#include <stdio.h>

int main(){
int inv1;
int inv2;
int inv3;
int inv4;

printf("Pleas enter the beginning inventory of Piels. \n");
scanf("%d", &inv1);
printf("Pleas enter the beginning inventory of Coors. \n");
scanf("%d", &inv2);
printf("Pleas enter the beginning inventory of Bud. \n");
scanf("%d", &inv3);
printf("Pleas enter the beginning inventory of Iron City. \n");
scanf("%d", &inv4);

printf("Please enter the ID number. \n Piels - 1 \n Coors - 2 \n Bud - 3 \n Iron City - 4 \n Enter -1 to exit \n"); 

int id;

scanf("%d", &id);
while( id != -1){

int amount;

    switch (id) {
    case '1': 
         printf("Enter the change in amount. It will be a negative if the amount is sold, or positive if the amount is purchased \n");
         scanf("%d", &amount);
         inv1 += amount;
         break;
    case '2': 
         printf("Enter the change in amount. It will be a negative if the amount is sold, or positive if the amount is purchased \n");
         scanf("%d", &amount);
         inv2 += amount;
         break;
    case '3': 
         printf("Enter the change in amount. It will be a negative if the amount is sold, or positive if the amount is purchased \n");
         scanf("%d", &amount);
         inv3 += amount;
         break;
    case '4': 
         printf("Enter the change in amount. It will be a negative if the amount is sold, or positive if the amount is purchased \n");
         scanf("%d", &amount);
         inv4 += amount;
         break;
    default:
        printf("Error: That ID Number is not an option. \n");
        break;
                  }


printf("Please enter the ID number. \n Piels - 1 \n Coors - 2 \n Bud - 3 \n Iron City - 4 \n Enter -1 to exit \n");
    scanf("%d", &id);
}
    return 0;

}

Answer 1

Remove quotes and try from switch condition

 switch (id) {
        case 1: 
             printf("Enter the change in amount. It will be a negative if the amount is sold, or positive if the amount is purchased \n");
             scanf("%d", &amount);
             inv1 += amount;
             break;
        case 2: 
             printf("Enter the change in amount. It will be a negative if the amount is sold, or positive if the amount is purchased \n");
             scanf("%d", &amount);
             inv2 += amount;
             break;
        case 3: 
             printf("Enter the change in amount. It will be a negative if the amount is sold, or positive if the amount is purchased \n");
             scanf("%d", &amount);
             inv3 += amount;
             break;
        case 4: 
             printf("Enter the change in amount. It will be a negative if the amount is sold, or positive if the amount is purchased \n");
             scanf("%d", &amount);
             inv4 += amount;
             break;
        default:
            printf("Error: That ID Number is not an option. \n");
            break;
                      }

Answer 2

由于您将输入读取为整数：

scanf("%d", &id); //note the %d

然后 id 将具有整数值，从您在控制台中输入的 string 转换而来。

Example: 
Input: 41 //this is char '4' and '1', having value of 0x34 (52) and 0x31 (49) respectively
Result: id = 41 //(not resulting in char* but value of 41)

如果你想使用字符，那么你应该这样做：

char id;
scanf(" %c", &id); //note the %c, might also be better if used with early space to avoid \n from the input buffer

这样它将把您的输入读取为字符

Example:
Input: 4 //this is char '4' (having value of 0x34 (52))
Result: id = '4' or id = 52 //not resulting in actual value of 4, but char '4' or value of 52 (0x34)

那么你的开关：

switch(id){
    case '4': //this has actual value of 52 (or 0x34), check ASCII table
        break;
    // and so on, 
}

会好的。

请注意，这会限制您对 '0'-'9' 的选择，因为它们是唯一可用的 ASCII 字符。

所以，还是用scanf("%d", &id);

最好

只需删除 switch 中的 ':

int id;
scanf("%d, &id);
switch(id){
    case 1: //this has actual integer value of 1, not ASCII '1' = 0x31 (or 49)
        break;
    // and so on, will be fine
}

那也行。

Answer 3

如代码所示，字符值和整数值之间似乎存在误解。

一个字符，如“1”，其值为 0x31。

而像 1 这样的整数值的值为 0x00000001。

对于 switch/cases，大小写值必须是整数，因此不要将这些值用单引号引起来，因为这些单引号表示字符文字而不是整数文字。

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