Counting work days between two dates in C - c

Question

I am writing a code in C with two functions.
The first (WorkDay) takes a date and says if it is a working day (return 1) or not (return 0). I think the first function is OK, although it could be better, but it is working. It includes weekends and public holidays in my country.
The problem comes with the second function (CountWorkDays). It should take two dates and say if they are correct (return 1) and in that case also say how many working days is among them, including the entered dates (cnt=). If the dates aren't correct (first is bigger than second etc.), there is return 0. I've tried to make a helping function next_day(), but I am pretty sure it is wrong. Can you help me with the second function please?
I cannot use <time.h> and I put there some asserts, which I am testing the function with.
#include <stdio.h>
#include <math.h>
#include <assert.h>
int WorkDay ( int y, int m, int d )
{
int h, day;
h= (d + floor(((m+1)*26)/10) + y + floor(y/4) + 6*floor(y/100) + floor(y/400));
day=h%7;
if ((y%4!=0) && m==2 && d==29)
return 0;
else if (((y%4==0 || y%400==0) && (y%100!=0 || y%4000!=0)) && m==2 && d==29)
{
if (day==2 || day==3 || day==4 || day==1 || day==0)
return 1;
else
return 0;
}
else if ((d==1 && m==1) || (d==1 && m==5) || (d==8 && m==5) || (d==5 && m==7) || (d==6 && m==7) || (d==28 && m==9) || (d==28 && m==10) || (d==17 && m==11) || (d==24 && m==12) || (d==25 && m==12) || (d==26 && m==12) || day==0 || day==1 || (m==1 && (d>31 || d<1)) || (m==2 && (d>29 || d<1)) || (m==3 && (d>31 || d<1)) || (m==4 && (d>30 || d<1)) || (m==5 && (d>31 || d<1)) || (m==6 && (d>30 || d<1)) || (m==7 && (d>31 || d<1)) || (m==8 && (d>31 || d<1)) || (m==9 && (d>30 || d<1)) || (m==10 && (d>31 || d<1)) || (m==11 && (d>30 || d<1)) || (m==12 && (d>31 || d<1)) || y<2000 || m>12 || m<1)
return 0;
else if (day==2 || day==3 || day==4 || day==5 || day==6)
return 1;
else
return 0;
}
int next_day()
{
int y1, m1, d1;
static int days_in_month[] = { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
unsigned short day_counter;
d1 += 1; day_counter++;
if (d1 > days_in_month[m1])
{
d1 = 1;
m1 += 1;
if (m1 > 12)
{
m1 = 1;
y1 += 1;
if (((y1%4==0 || y1%400==0) && (y1%100!=0 || y1%4000!=0)))
{
days_in_month[2] = 29;
}
else
{
days_in_month[2] = 28;
}
}
}
return 0;
}
int CountWorkDays ( int y1, int m1, int d1,
int y2, int m2, int d2,
int * cnt )
{
int i,x;
if ( (m1==1 && (d1>31 || d1<1)) || (m1==2 && (d1>29 || d1<1)) || (m1==3 && (d1>31 || d1<1)) || (m1==4 && (d1>30 || d1<1)) || (m1==5 && (d1>31 || d1<1)) || (m1==6 && (d1>30 || d1<1)) || (m1==7 && (d1>31 || d1<1)) || (m1==8 && (d1>31 || d1<1)) || (m1==9 && (d1>30 || d1<1)) || (m1==10 && (d1>31 || d1<1)) || (m1==11 && (d1>30 || d1<1)) || (m1==12 && (d1>31 || d1<1)) || y1<2000 || m1>12 || m1<1 ||(m2==1 && (d2>31 || d2<1)) || (m2==2 && (d2>29 || d2<1)) || (m2==3 && (d2>31 || d2<1)) || (m2==4 && (d2>30 || d2<1)) || (m2==5 && (d2>31 || d2<1)) || (m2==6 && (d2>30 || d2<1)) || (m2==7 && (d2>31 || d2<1)) || (m2==8 && (d2>31 || d2<1)) || (m2==9 && (d2>30 || d2<1)) || (m2==10 && (d2>31 || d2<1)) || (m2==11 && (d2>30 || d2<1)) || (m2==12 && (d2>31 || d2<1)) || y2<2000 || m2>12 || m2<1 || y2>y1 || (y1==y2 && m2>m1) || (y1==y2 && m1==m2 && d2>d1) )
return 0;
else
{
while (y1!=y2 && m1!=m2 && d1!=d2)
{
while (next_day())
{
if (WorkDay( y1, m1, d1 ) == 1)
i=0;
x=i++;
}
}
*cnt=x;
return 1;
}
}
int main ( int argc, char * argv [] )
{
int cnt;
assert ( WorkDay ( 2016, 11, 11 ) );
assert ( ! WorkDay ( 2016, 11, 12 ) );
assert ( CountWorkDays ( 2016, 11, 1,
2016, 11, 30, &cnt ) == 1
&& cnt == 21 );
assert ( CountWorkDays ( 2001, 1, 1,
2015, 2, 29, &cnt ) == 0 );
return 0;
}

Answer 1

The problem is in next_day() and CountWorkDays().
next_day() is using local variables d1, m1 and y1. It is calculating next day of some random day.
In CountWorkDays(), you are not incrementing d1, m1, y1.
Solution:
Modify next_day() to receive a day as input and return next day as output.
int next_day(int *d, int *m, int *y)
{
/* Use current day to start. */
int y1 = *y;
int m1 = *m;
int d1 = *d;
/* Your code to find next day. Remove day_counter here as it is unnecessary.*/
/* Return next day. */
*y = y1;
*m = m1;
*d = d1;
return 0;
}
In CountWorkDays() call next_day with d1, m1, y1 as below.
else
{
while (1)
{
if (y1!=y2 && m1!=m2 && d1!=d2) //Check if end day is reached.
{
if (WorkDay( y1, m1, d1 ) == 1)
x++; //At the beginning initialize x to 0.
}
else
{
break;
}
next_day(&d1, &m1, &y1); //Get the next day.
}
}

Answer 2

int CountWorkDays(int y1, int m1, int d1, int y2, int m2, int d2, int * cnt)
{
int i, x;
if( (m1 == 1 && (d1>31 || d1<1)) || (m1 == 2 && (d1>29 || d1<1)) || (m1 == 3 && (d1>31 || d1<1)) || (m1 == 4 && (d1>30 || d1<1)) || (m1 == 5 && (d1>31 || d1<1)) || (m1 == 6 && (d1>30 || d1<1)) || (m1 == 7 && (d1>31 || d1<1)) || (m1 == 8 && (d1>31 || d1<1)) || (m1 == 9 && (d1>30 || d1<1)) || (m1 == 10 && (d1>31 || d1<1)) || (m1 == 11 && (d1>30 || d1<1)) || (m1 == 12 && (d1>31 || d1<1)) || y1<2000 || m1>12 || m1<1 ||
(m2 == 1 && (d2>31 || d2<1)) || (m2 == 2 && (d2>29 || d2<1)) || (m2 == 3 && (d2>31 || d2<1)) || (m2 == 4 && (d2>30 || d2<1)) || (m2 == 5 && (d2>31 || d2<1)) || (m2 == 6 && (d2>30 || d2<1)) || (m2 == 7 && (d2>31 || d2<1)) || (m2 == 8 && (d2>31 || d2<1)) || (m2 == 9 && (d2>30 || d2<1)) || (m2 == 10 && (d2>31 || d2<1)) || (m2 == 11 && (d2>30 || d2<1)) || (m2 == 12 && (d2>31 || d2<1)) || y2<2000 || m2>12 || m2<1 ||
y2>y1 || (y1 == y2 && m2>m1) || (y1 == y2 && m1 == m2 && d2>d1))
...
x++;
Your logic is wrong and redundant. You need to check only once if day is less than 1. You are checking at least 20 times. Then you check it again another 20 times in another function. You repeat that for d2. This makes your code unreadable and prone to errors.
Also you are not initializing variables. The starting value of x is undefined. Put int x = 0; and i = 0;
Later you have:
i=0;
x=i++;
You could rewrite this as x = 1. But you probably mean to write x++
Here it seems you are checking for holidays:
else if((
d == 1 && m == 1) ||
(d == 1 && m == 5) ||
(d == 8 && m == 5) ||
(d == 5 && m == 7) ||
(d == 6 && m == 7) ||
(d == 28 && m == 9) ||
(d == 28 && m == 10) ||
(d == 17 && m == 11) ||
(d == 24 && m == 12) ||
(d == 25 && m == 12) ||
(d == 26 && m == 12) ||
This type of coding is not wrong, but it's not practical either. I would put the holidays in a structure:
struct holidays_t
{
int day, month;
};
struct holidays_t holidays[] = {
{ 1 , 1 },
{ 1 , 5 },
...
};
Then loop through holidays array to see if the dates match. If you have not learned structures yet, then put the days and months in two different arrays. Example:
int holiday_days[]={1,1,...};
int holiday_months[]={1,5,...};
Your formula for weekday is wrong. You need to fix that.
#include <stdio.h>
#include <math.h>
int is_leap_year(int y)
{
return (y % 4) == 0 && y % 100 != 0 || (y % 400 == 0 && y != 4000);
}
int get_days_in_month(int year, int month)
{
const int days_in_month[] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
if(month >= 1 && month <= 12)
{
int days = days_in_month[month - 1];
if(month == 2 && is_leap_year(year))
days++;
return days;
}
return 0;
}
int is_date_valid(int year, int month, int day)
{
if(get_days_in_month(year, month) == 0) return 0;
return day >= 1 && day <= get_days_in_month(year, month);
}
//this is wrong: ***************************************************
int get_weekday(int y, int m, int d)
{
int h = (d + floor(((m + 1) * 26) / 10) + y + floor(y / 4) + 6 * floor(y / 100) + floor(y / 400));
int weekday = h % 7;
return weekday;
}
struct holidays_t
{
int day, month;
};
int is_holiday(int m, int d)
{
const struct holidays_t holidays[] = {
{ 1 , 1 },
{ 1 , 5 },
{ 8 , 5 },
{ 5 , 7 },
{ 6 , 7 },
{ 28, 9 },
{ 28, 10 },
{ 17, 11 },
{ 24, 12 },
{ 25, 12 },
{ 26, 12 },
};
int count = sizeof(holidays) / sizeof(holidays[0]);
int i;
for(i = 0; i < count; i++)
if(holidays[i].month == m && holidays[i].day == d)
return 1;
return 0;
}
int CountWorkDays(int y1, int m1, int d1, int y2, int m2, int d2, int *ptr)
{
int count = 0;
*ptr = 0;
if(!is_date_valid(y1, m1, d1)) return 0;
if(!is_date_valid(y2, m2, d2)) return 0;
int y, m, d;
for(y = y1; y <= y2; y++)
{
int month_start = 1;
int month_end = 12;
if(y == y1) month_start = m1;
if(y == y2) month_end = m2;
for(m = month_start; m <= month_end; m++)
{
int day_start = 1;
int day_end = get_days_in_month(y, m);
if(y == y1 && m == m1) day_start = d1;
if(y == y2 && m == m2) day_end = d2;
for(d = day_start; d <= day_end; d++)
{
int test = 0;
if(is_holiday(m, d))
{
test = 1;
printf("holiday %d %d %d\n", y, m, d);
}
int weekday = get_weekday(y, m, d);
if(weekday == 0 || weekday == 6)
{
test = 1;
printf("weekend %d %d %d %s\n", y, m, d, (weekday == 0) ? "sunday" : "staurday");
}
if(!test)
{
count++;
}
}
}
}
*ptr = count;
//return success
return 1;
}
int main()
{
int count = 0;
CountWorkDays(2016, 1, 1, 2016, 12, 31, &count);
printf("count %d\n", count);
return 0;
}