如何使用 strcmp() 将输入与多个字符串（字符串数组）进行比较？ [复制]

Question

这是我目前的代码

#include <stdio.h>
#include <string.h>  

int main() {
    char size[10];
    const char drinks[4][10] = {
        "Coffee",
        "Tea",
        "Chocolate",
        "Soda"
    };
    const char sizes[3][10] = {
        "Small",
        "Medium",
        "Large"
    };
    char drinksName[10];
    do {
        printf("\nDrinks name: ");
        scanf("%s", drinksName);
        if (strcmp(drinksName, drinks[0]) != 0 || strcmp(drinksName, drinks[1]) != 0 || strcmp(drinksName, drinks[2]) != 0 || strcmp(drinksName, drinks[3]) != 0) {
            printf("Not available.");
        }
    } while (strcmp(drinksName, drinks[0]) != 0 || strcmp(drinksName, drinks[1]) != 0 || strcmp(drinksName, drinks[2]) != 0 || strcmp(drinksName, drinks[3]) != 0);
    do {
        printf("\nSize: ");
        scanf("%s", size);
        if (strcmp(size, sizes[0]) != 0 || strcmp(size, sizes[1]) != 0 || strcmp(size, sizes[2]) != 0) {
            printf("Not available.");
        }
    } while (strcmp(size, sizes[0]) != 0 || strcmp(size, sizes[1]) != 0 || strcmp(size, sizes[2]) != 0);
}

当我尝试运行我的程序时，输入总是循环，而我的输入为真，例如：“咖啡”。我的循环代码有错误吗？

do {
        printf("\nDrinks name: ");
        scanf("%s", drinksName);
        if (strcmp(drinksName, drinks[0]) != 0 || strcmp(drinksName, drinks[1]) != 0 || strcmp(drinksName, drinks[2]) != 0 || strcmp(drinksName, drinks[3]) != 0) {
            printf("Not available.");
        }
    } while (strcmp(drinksName, drinks[0]) != 0 || strcmp(drinksName, drinks[1]) != 0 || strcmp(drinksName, drinks[2]) != 0 || strcmp(drinksName, drinks[3]) != 0);

我很困惑为什么会这样。

Answer 1

如果您的输入与 其中一个元素不同，则您的代码意味着继续循环。这个条件永远成立，因为有不同的元素。

您应该使用&&（逻辑与）运算符而不是||（逻辑或）运算符来检查您输入的元素是否与所有元素不同，如下所示：

do {
    printf("\nDrinks name: ");
    if (scanf("%9s", drinksName) != 1) {
        fputs("Read error.\n", stderr);
        return 1;
    }
    if (strcmp(drinksName, drinks[0]) != 0 && strcmp(drinksName, drinks[1]) != 0 && strcmp(drinksName, drinks[2]) != 0 && strcmp(drinksName, drinks[3]) != 0) {
        printf("Not available.");
    }
} while (strcmp(drinksName, drinks[0]) != 0 && strcmp(drinksName, drinks[1]) != 0 && strcmp(drinksName, drinks[2]) != 0 && strcmp(drinksName, drinks[3]) != 0);

另外请注意，您应该指定要读取的字符串的最大长度以避免缓冲区溢出，并检查scanf()的返回值以检查是否读取成功。

另一种选择是使用循环来查找匹配的元素，如下所示：

int matchFound;
do {
    printf("\nDrinks name: ");
    if (scanf("%9s", drinksName) != 1) {
        fputs("Read error.\n", stderr);
        return 1;
    }
    matchFound = 0;
    for (size_t i = 0; i < sizeof(drinks) / sizeof(drinks[0]); i++) {
        if (strcmp(drinksName, drinks[i]) == 0) {
            matchFound = 1;
            break;
        }
    }
    if (!matchFound) {
        printf("Not available.");
    }
} while (!matchFound);