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/*
* Based on the year 2000/01/01,when is Saturday to finger out the Y/M/01 's weekday,if we know this,we
* can print all that month's weekdays.
*/
#include "stdio.h"
#define USHORT unsigned short
#define ULONG unsigned long
USHORT DaysOfEachMonth[12] = {31,28,31,30,31,30,31,31,30,31,30,31};/* the common days of each month,not the leap year */
USHORT Total[12] = {0,31,59,90,120,151,181,212,243,273,304,334};
USHORT M = 0;/* month */
ULONG Y = 0;/* Year */
USHORT IsLeapYear(ULONG year); /* Judge the year is a leep year(return 1) or not(return 0) */
USHORT WeakDayOfYM1();/* Count the weakday of Y/M/1 */
void Print(USHORT space);
unsigned short IsLeapYear(ULONG year)
{
return((year%4 == 0 && year%100) || year%400 == 0)?1:0;
}
USHORT WeakDayOfYM1()
{
ULONG Range_Y = 0, Sub_N = 0;
USHORT Div_Y = 0, Div_M = 0, Space = 0, TotalDays = 0, Flag = 0;
short Div = 0;/* use unsigned short Div may < 0 */
Flag=(Y==2000)?0:((Y>2000 || IsLeapYear(Y))?2:1);/* we donot Judge the year Y, if Y=2000,we Flag=0
* if the year>2000 or the year is a leep year
* Flag=2,else Flag=1
* this is the key!! */
Range_Y = (Y>2000)?(Y-2001):((Y<2000)?(2000-Y-1):0); /* not include the year Y */
Sub_N = Range_Y/4 - Range_Y/100 + Range_Y/400;/* num of leap year */
Div_Y = 2*Sub_N%7 + (Range_Y - Sub_N + Flag)%7;/* offset between 2000/01/01 and Y/01/01,
* eacn leap year has 366 days the offset is 366%7=2,
* so we use 2*Sub_N, and the other years which are not
* leap year, the offset is 365%7=1,so we use Range_Y-Sub_N
* do not use Div_Y = (2*Sub_N + Range_Y - Sub_N + Flag)%7;
* defend overflow.
*/
TotalDays=Total[M-1];/* the total days from January to Month M */
if(IsLeapYear(Y) && M>=3)
TotalDays++; /* Yet we donot Judge the year Y, now we do it,if Y is a leap year and M is big
* than 29,Februray, we increase the totaldays,because the default days of Feb is
* 28 */
Div_M=TotalDays%7;/* offset between Y/01/01 and Y/M/01 */
Div=(Y>2000)?(Div_M+Div_Y)%7:(Div_M-Div_Y)%7; /* offet between 2000/01/01 and Y/01/01
* there is a puzzle puzzled me so long,when
* Y=1900,M=1 or 2 or 3 ...,u will see Div_M=0,Div_Y=5,but
* the result of Div=4!!! this happend in Turbo C 2.0
* but in gcc and Dev-C++ and VS 2005 that's OK,so surprised thing!!!
*/
Space=(6 + Div)%7;/* the number 6 is the weekday of 2000/01/01-Saturday,also is the init offset */
return Space;/* return the result offset we do want */
}
void Print(USHORT space)
{
USHORT days=DaysOfEachMonth[M-1],i=0,j=0;
printf("\t\t********==== Calendar ====********\n");
printf("\t\t*************F.U.Moon*************\n");
printf("\t\t\t %lu/%-2hu \n\n",Y,M);
printf("\tSun\tMon\tTue\tWen\tThu\tFri\tSat\n");
for(i=0;i<space;i++)
printf("\t");
if(IsLeapYear(Y) && M == 2)
days=29;
for(j=1;j<=days;j++)
{
printf("\t%3d",j);
if((space + j)%7 == 0)
printf("\n");
}
}
int main(int argc, char* argv[])
{
USHORT space = 0;
printf("Input Year and Month:");
scanf("%lu%hu",&Y,&M);/* we do not check the input */
space = WeakDayOfYM1();
Print(space);
fflush(stdin);/* flush the stdin,if not do this some compile need two getchar(); */
getchar();
return 0;
}
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