problem 19

/*You are given the following information, but you may prefer to do some research for yourself.

1 Jan 1900 was a Monday.
Thirty days has September,
April, June and November.
All the rest have thirty-one,
Saving February alone,
Which has twenty-eight, rain or shine.
And on leap years, twenty-nine.
A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.
How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?
*/
#include <iostream>
#include<string>
#include<math.h>
using namespace std;


// check leap year
bool checkleap(int years){
 if(years % 4 == 0  && years % 400 != 0){
    return true ;
 }
 return false;
}


int main(){
int sunday = 0;
int weekday = 2; // first day we start with is Tuesday
int counter = 0;
int month_len [13] = {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
  for(int years = 1901; years  < 2001; years++){
    if(checkleap(years)){
      month_len[2] = 29;
    }
    else{
      month_len[2] = 28;
    }
    for(int months = 1; months <= 12; months++){
       for(int days = 1; days <= month_len[months]; days++){
          weekday = weekday % 7;
          if(weekday == sunday && days == 1){
           counter = counter + 1;
          }
          weekday++;
       }
     }
    }
  cout << counter <<endl;
  return 0;
}