《c程序设计语言》读书笔记-5.8-天数和日期转换错误检查

#include "stdio.h"
#include "stdlib.h"
#include "string.h"

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}
};

int day_of_year(int year,int month,int day)
{
    int i,leap;

    leap = ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0);
    if(month < 1 || month > 12)
        return -1;
    if(day < 1 || day > daytab[leap][month])
        return -1;
    for(i = 1;i < month;i++)
        day += daytab[leap][i];

    return day;
}

void month_day(int year,int yearday,int *pmonth,int *pday)
{
    int i,leap;

    if(year < 1)
    {
        *pmonth = -1;
        *pday = -1;
        return;
    }
    leap = ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0);
    for(i = 1;i <= 12 && yearday > daytab[leap][i];i++)
        yearday -= daytab[leap][i];

    if(i > 12 && yearday > daytab[leap][12])
    {
        *pmonth = -1;
        *pday = -1;
    }
    else
    {
        *pmonth = i;
        *pday = yearday;
    }
}
int main()
{
    int n;
    int month = 0,day = 0;
    int *pmonth = &month,*pday = &day;

    n = day_of_year(2014,11,14);
    printf("%d\n",n);

    month_day(2014,318,pmonth,pday);
    printf("%d %d",*pmonth,*pday);

    return 0;
}

这个程序中，得到的注意事项：指针必须初始化，否则后果很严重。。不过我现在还不知道到底什么严重个后果。。。