c - 我无法理解的几个错误

Question

所以我写了这个:

#include <stdio.h>
#define _CRT_SECURE_NO_WARNINGS

int main() {
    float balance;
    char type;

    printf("Card balance: ");
    scanf("%f", &balance);

    do {
        printf("Vehicle type: ");
        scanf("%c", &type);
        if (type != 'B' || type != 'b' || type != 'C' || type != 'c' || type != 'T' || type != 't') {
            printf("Incorrect vehicle type!");
        }
    } while(type != 'B' || type != 'b' || type != 'C' || type != 'c' || type != 'T' || type != 't') ;

    system("pause");
    return 0;
}

当我尝试运行它时，出现了这些错误:

1.scanf: This function or variable may be unsafe. Consider using scanf_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS.

2.system undefined; assuming extern returning int

Answer 1

scanf 将变量的地址作为参数。所以，你需要做

scanf("%f", &balance);
scanf("%c", &type);

对于system，你需要包含stdlib.h