Lesson 13 Sorry, your car is restricted today 对不起，你的车今天限行

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

enum 
{ 
    MONDAY=1, 
    TUESDAY, 
    WEDNESDAY, 
    THURSDAY, 
    FRIDAY,
    SATURDAY,
    SUNDAY
};

int is_restricted(int num, int today)
{
    int ret;
    
    switch (num)
    {
        case 0:
        case 5:
            ret = (today == MONDAY) ? 1 : 0;
            break;
            
        case 1:
        case 6:
            ret = (today == TUESDAY) ? 1 : 0;
            break;
            
        case 2:
        case 7:
            ret = (today == WEDNESDAY) ? 1 : 0;
            break;
            
        case 3:
        case 8:
            ret = (today == THURSDAY) ? 1 : 0;
            break;
            
        case 4:
        case 9:
            ret = (today == FRIDAY) ? 1 : 0;
            break;    
            
        default:    
            ret = 0;
            break;    
    }            

    return ret;
}

int main(int argc, char *argv[])
{
    char car_num_str[8] = "N2LG20";
    int tail_num;
    int result;
    
    printf("Please input your car number : \n");
    scanf("%s", car_num_str);
    
    printf("Your car number is <%s> \n", car_num_str);
    tail_num = car_num_str[strlen(car_num_str)-1] - '0';

    printf("the tail number is %d\n", tail_num);
    printf("Today is %s\n", __DATE__);
    
    result = is_restricted(tail_num, MONDAY);
    printf("Total your car is %s \n", result? "restricted" : "permitted");
    
    return 0;
}
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知识点

• 枚举 enum
• 分支语句 switch-case
  • break 用法
  • 格式的缩进和对齐
• switch-case 的应用场合
  • 状态机编程
  • printf 函数实现

课堂讨论

• 除了示例中的写法，如果不用 switch-case ，解决这个问题还有其他写法吗？
• 如果考虑到每3个月换一次尾号限行制度，这个程序应该怎么改？

课后练习

• 编写一个程序，统计各个数字，空白字符和其他所有字符出现的次数，以及行数。
• 分析一条格式化打印语句中，打印整数%d，字符%c，字符串%s，地址%p 各自出现的次数。