看不懂怎么过的

#include<bits/stdc++.h>
#define int /*unsigned */long long
using namespace std;
int y[]={0,31,28,31,30,31,30,31,31,30,31,30,31};
signed main(){
	ios::sync_with_stdio(0);
	cin.tie(0); cout.tie(0);
    int day,month;
    char t;
    cin>>day>>t>>month;
    //一月一日是星期五，倒退month月day日是星期几
    int hday=0;
    for(int i=1;i<month;i++)//计算month前面的月份总天数
        hday+=y[i];
    hday+=day-1;//计算从一月一日到month月day日有多少天
    int x=(hday+5-1)%7;
    if(x==0)//特判
        x=7;
    cout<<x;
	return 0;}