计算指定日期是该年份的第多少天

#include <iostream>
using namespace std;

int Sum(int year,int mon, int day)
{
int k, l;
int tab[2][13] = {{0,31,28,31,30,31,30,31,31,30,31,30,31},{0,30,29,31,30,31,30,31,31,30,31,30,31}};
k = ((year%4==0 && year%100!=0) || (year %400 == 0));
for (l=0; l<mon; l++)
{
day += tab[k][l];
}

return day;
}

int main()
{
int year, mon, day;
cin>>year>>mon>>day;
int sum = Sum(year, mon, day);

cout<<sum<<endl;

return 0;
}