黑色星期五

include <bits/stdc++.h>

using namespace std;
int a[13]={0, 31, 28, 31, 30, 31, 30, 31,31, 30, 31, 30, 31};
int main()
{
int day=4,b, n=0;
cin >> b;
if (b>1998)
{
for (int i=1998;i<b;i++)
{
if ((i%40&&i%100!=0)||i%4000)
{
day+=366;
}
else
{
day+=365;
}
day=day%7;
}
}
if ((b%40&&b%100!=0)||b%4000)
{
a[2]=29;
}
for (int i=1;i<=12;i++)
{
if ((day+13)%7-1==5)//反思1
{
n++;
}
day+=a[i];
day=day%7;
}
cout << n;
}
反思一：算天数时一定！一定！一定！要看清楚变量是什么！！！