c language perpetual calendar program code

#include <stdio.h>
 
int year(int y)
{
	if ((y%4==0) && (y%100!=0) || y%400==0)
		return 366;
	else
		return 365;
}
 
int main()
{
	int y;
	int i,j,sum=0;	
	int begin,week;
	int days[12]={31,28,31,30,31,30,31,31,30,31,30,31};
 
	scanf("%d",&y);
	for(i=1;i<y;i++)
		sum+=year(i);
	
	week=(sum+1)%7;		//表示该年1月1日为星期几
	
	if(year(y)==366)
		days[1]=29;	
 
	printf("\n%d年日历如下：\n\n",y);
 
	for(i=0;i<12;i++)
	{
		printf("       %d月          \n",i+1);
		printf("  7  1  2  3  4  5  6\n");
		printf("=====================\n");
		begin=1;
		for(j=0;j<week;j++)
			printf("   ");
		while(begin<=days[i])
		{
			printf("%3d",begin);
			begin++;
			week=(week+1)%7;
			if(week%7==0)
				printf("\n");
		}
		printf("\n\n");
 
	}
	
	return 0;
}