二维数组的名字

引用自知乎

#include 
#include 
#include 

static char daytab[2][13] = {
    {0,31,28,31,30,31,30,31,31,30,31,30,31},
    {0,31,29,31,30,31,30,31,31,30,31,30,31},
};

static char *name[] = {
    "Illegal month",
    "January", "February", "March",
    "April", "May", "June", "July",
    "August", "September", "October",
    "November", "December"
};


int date_to_day_point(int year, int month, int day);
void day_to_date_point(int year, int yearday, int *pmonth, int *pday);
char *month_name(int n);

int main() {
    int year = 2019, month = 7, day = 20;
    printf("%d年%d月%d号是今年第%d天.\n",year, month, day,date_to_day_point(year, month, day));
    int yearday = 201;
    int month_1, day_1;
    day_to_date_point(year, yearday, &month_1, &day_1);
    printf("%d年第%d天是今年的%d月%d号.\n", year, yearday, month_1, day_1);
    printf("%s\n", month_name(month_1));
    printf("%s\n", name[2]);
    return 0;
}

int date_to_day_point(int year, int month, int day) {
    int leap;
    char *p;
    leap = (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0);
    p = daytab[leap];
    while (--month) {
        day += *++p; //因为*p = 0存在,先++
    }
    return day;
}

void day_to_date_point(int year, int yearday, int *pmonth, int *pday) {
    int leap;
    char *p;
    leap = (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0);
    p = daytab[leap];
    while (yearday >= *++p) {
        yearday -= *p; //已经++了
    }
    *pmonth = p - *(daytab + leap); //重点！！！！！！！！！！！
    *pday = yearday;
}

char *month_name(int n) {
    return (n < 1 || n > 12) ? name[0] : name[n];
}

注意这行代码
*pmonth = p - *(daytab + leap); //重点！！！！！！！！！！！)