C++ แสดงวันของปี

int day, month, year;
int x=0;
cout << "Input {day month year} : ";
cin >> day >> month >> year;

if (month == 1)
{
day += 0;
}
else if (month == 2)
{
day = day + 31 ;
}
else if (month == 3)
{
day =  day + 31 + 28;
}
else if (month == 4)
{
day = day  + 31 + +28 + 30;
}
else if (month == 5)
{
day = day  + 31 +28 +  30 + 31;
}
else if (month == 6)
{
day = day  + 31 + 28 + 30 + 31 + 30;
}
else if (month == 7)
{
day = day + 31 + 28 + 30 + 31 + 30 + 31 ;
}
else if (month == 8)
{
day = day + 31 + 28 + 30 + 31 + 30 + 31 + 31;
}
else if (month == 9)
{
day = day +  31 + 28 + 30 + 31 + 30 + 31 + 31 + 30;
}
else if (month == 10)
{
day = day +  31 + 28 +  30 + 31 + 30 + 31 + 31 + 30 + 31;
}
else if (month == 11)
{
day = day + 31 + 28 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30;
}
else if (month == 12)
{
day = day +  31 + 28 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30 + 31;
}
if (year % 2 == 1 && month > 2)
day = day + 1;
cout << day << endl;