C + + style write to judge a certain day of the year is one of the first days of the year

Beginner C + +, writing functions in structs and some of the formats required by some C + + languages

Look at the code

#include <iostream>
#include <cstdio>
using namespace Std;

struct What_day
{
int year;
int month;
int day;
void count (int year,int month,int Day)
{
int s[12]={0,31,28,31,30,31,30,31,31,30,31,30};
int sum=day;
for (int i=0;i<month;i++)
{
Sum=sum+s[i];
}
if (year%400| | (year%4==0&&year%100)) &&MONTH>2)
{
sum++;
}
cout<<sum<<endl;
}
};

int main ()
{
cout<< "Please input year month" <<endl;
What_day num;
cin>>num.year>>num.month>>num.day;
Num.count (Num.year,num.month,num.day);
return 0;
}

C + + style write to judge a certain day of the year is one of the first days of the year