通过c语言的指针来访问和运算

#include<stdio.h>
#include<string.h>
typedef struct{
	int year;
	int month;
	int day;
}DAY,*SD;

int main(){
	SD sd=(SD)malloc(sizeof(DAY));
	if(sd==NULL) return 0;
	int arr[12]={31,28,31,30,31,30,31,31,30,31,30,31};
	
	scanf("%d %d %d",&(sd->year),&(sd->month),&(sd->day));
	if((sd->year)%4==0 && (sd->year)%100!=0 ||(sd->year)%400==0){
		arr[1]=29;
	}
	int days=0;
	for(int i=0;i<sd->month-1;i++){
		days+=arr[i];
	}
	printf("%d",days+(sd->day));
	return 0;
}