workDay

Calculates the next work day that is a number days from nDate. holidays and weekends are assumed not to be workdays and are excluded.

If days is set to zero then this function will simply return nDate regardless of weather is lies on a holiday (or weekend). This functionality may seem strange, however, without some directional bias, it is impossible to know if you should move forward to Monday or backward to Friday. This emulates Excel's interpretation of the function.

In solving this problem you could iterate through each day until you had counted a sufficient number of workable days. For example:

while(days>0)
{
  int h;
  for(h=0;h<holidays && holidayDates[h]!=nDate;h++);  // check against holiday list
  if(h==holidays) days--;                             // only decrement if not a holiday
  nDate=nextWeekDay(nDate);                           // find next week day
}

This approach is applied by certain spreadsheet applications we emulate, unfortunately the time taken by this function scales linearly with size of days. We have opted for a constant time method, which although more involved, works in the following fashion:

s=daysOfWeek(nDate)
nDate-= s;              // move to beginning of current week.
...
days+=s;
nDate+= (days/5) * 7;   // add whole weeks
nDate+= d%5;            // add remainder within week

We then count the number of holidays within this new date range, and advance forward using the slow method shown above (in C++). However, the majority of the work has been done by this point - so the overall scheme is far faster.

workDay(date("1 jan 5"), 0);     // returns Saturday 1 January 2005
workDay(date("1 jan 5"), 1);     // returns Monday 3 January 2005
workDay(date("1 jan 5"), 1, 1);  // returns Tuesday 4 January 2005 (Monday is assumed a holiday)
workDay(date("1 jan 5"), 2);     // returns Monday 3 January 2005

#include <stdio.h>
#include <codecogs/units/date/workday.h>
#include <codecogs/units/date/dateymd.h>
#include <codecogs/units/date/date.h>
#include <codecogs/units/date/nextweekday.h>

using namespace Units::Date;

void main()
{
int holidays[3];
holidays[0]=date(2005, 1, 1);            // New years day
holidays[1]=date(2004,12,25);            // Christmas day
holidays[2]=nextWeekDay(holidays[2]);    // Boxing day or first weekday after Christmas

printf("\n StartDate   days   newDate");
int startdate=date("1 jan 2005");
for(int i=-50;i<50;i+=10)
{
  int d,m,y;
  dateYMD(startdate,y,m,d);
  printf("\n %2d-%2d-%d",d,m,y);
  
  dateYMD(workDay(startdate, i, 3, holidays),y,m,d);
  printf("  %2d   %2d-%2d-%d", i, d,m,y);
}
}

StartDate   days   newDate
1- 1-2005  -50   22-10-2004
1- 1-2005  -40    5-11-2004
1- 1-2005  -30   19-11-2004
1- 1-2005  -20    3-12-2004
1- 1-2005  -10   17-12-2004
1- 1-2005    0    1- 1-2005
1- 1-2005   10   14- 1-2005
1- 1-2005   20   28- 1-2005
1- 1-2005   30   11- 2-2005
1- 1-2005   40    1- 3-2005

Parameters