According to the discussion board.
I reference one code on here and change some thing.
But why still got the wrong answer.
I use the sample test to test.
The answer is right.
But when I upload to judgement.
Alway got the WA #1.

Someone can tell me why.
Thank you.

Below is my code.

#include<stdio.h>
#include<stdlib.h>

int is_leap_year(int y){
      return (  ( y%4==0 ) && (y%100!=0||y%400==0)  );
}


int days_per_year(int y){

      if(is_leap_year(y))
            return 366;
      else
            return 365;
}

int days_per_month(int m,int y){

      const int days[12]={31,28,31,30,31,30,31,31,30,31,30,31};
      if(m!=2)
             return days[m-1];
      else if(is_leap_year(y))
             return 29;
      else
             return 28;
}

int get_day_of_week(int m,int d,int y){
    int day=4;  /*  Key point  */
    int i;

      for(i=1600;i<y;i++) day+=days_per_year(i);
      for(i=1;i<m;i++) day+=days_per_month(i,y);
      day+=d;


return day%7;
}

void print_calendar(int m,int d,int y)
{
      const char* day_name[7]={"mon","tue","wed","thu","fri","sat","sun"};
      int days=days_per_month(m,y);
      int day_begin=1-get_day_of_week(m,1,y);

      int more_print = (day_begin + days)%7;

      int i,j,flag;


      flag = 0;
      for(i=0;i<7;i++){
          printf("%s",day_name[i]);

          for(j=day_begin+i ; j <= days + more_print ; j+=7 )

                if(  j<1   ||   j>days   )
                    printf("....");

                else if(j==d){
                        flag = 1;
                        if(j<10)
                           printf("..[%d]",j);
                        else
                           printf("..[%2d]",j);
                }
                else{
                              if(j<day_begin+7){
                                  if(flag){
                                     printf("..%d",j);
                                     flag = 0 ;
                                  }
                                  else{
                                    printf("...%d",j);
                                  }
                              }
                              else if(j >= day_begin+7 && j<10){
                                  if(flag){
                                     printf("...%d",j);
                                     flag = 0 ;
                                  }
                                  else{
                                    printf("....%d",j);
                                  }
                              }
                              else if(j>=10 && j<= days){
                                  if(flag){
                                     printf("..%2d",j);
                                     flag = 0 ;
                                  }
                                  else{
                                    printf("...%2d",j);
                                  }
                              }
                              else{
                                    printf("....");

                              }
                }/* if(  j<1   ||   j>days   )  */

                 printf("\n");
      }/* for(i=0;i<7;i++) */

}


int main()
{
    int d,m,y;
    scanf("%d %d %d",&d,&m,&y);

    if( y < 1600 || y > 2400) exit(0);
    if( m < 1 || m > 12 ) exit(0);
    if( d < 1 || d > 31 ) exit(0);

    print_calendar(m,d,y);


exit (0);
}