Here’s the problem:

How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?

And here’s my code:

#include <stdio.h>  int main(void){     int months[12] = { 31 , 28 , 31 , 30 , 31 , 30 , 31 , 31 , 30 , 31 , 30 , 31 };     int year=1901;     int dayoftheweek=2;  //put a 2 because the 1 jan 1901 is tuesday. 0-sunday 6-Saturday     int sunday=0;     int firstsundays=0;      while(year<=2000){         if(year%4==0)    //checking if it's a leap year             months[1]=29;          for (int i = 0; i < 12; ++i) {             for (int d = 1; d < months[i]; d++){                 if(dayoftheweek==7)  //reset the week                     dayoftheweek=0;                  if(dayoftheweek==sunday && d==1)                     firstsundays++;                  dayoftheweek++;             }         }          months[1]=28;         year++;     }      printf("There are %d Sundays that fell on the first of the month\n", firstsundays);      return 0; } 

The asnwer to this problem is 171 but my program gives 170, why is that? In the meantime what could I improve?