How to add only some days to date-time variable?

Question

When I need to increase date 1/1/2016 by 7 days, I can simply do:

IncDay(myDate, 7); // Result 8/1/2016

What do I do, if I need to ignore some days (e.g. Saturdays), so the Result is 10/1/2016 ?

Answer 1

This adds a day to the calculation for each Saturday found in the ANumberOfDays range:

{.$DEFINE UNCLEAR_WHAT_YOU_R_ASKING}

function IncDayIgnoringSaturdays(const AValue: TDateTime; const ANumberOfDays: Integer = 1): TDateTime;
var
  i, j: Integer;
begin
  i := ANumberOfDays;
  j := 0;
  Result := AValue;
  while i > 0 do begin
    Result := IncDay(Result);
    if DayOfTheWeek(Result) = DaySaturday then
      Inc(j);
    Dec(i);
  end;
  Result := IncDay(Result, j);

  {$IFDEF UNCLEAR_WHAT_YOU_R_ASKING}
  if DayOfTheWeek(Result) = DaySaturday then
    Result := IncDay(Result);
  {$ENDIF}
end;

begin
  WriteLn(DateTimeToStr(IncDayIgnoringSaturdays(StrToDateTime('1/1/2016'), 7)));
  WriteLn(DateTimeToStr(IncDayIgnoringSaturdays(StrToDateTime('1/1/2016'), 14)));
  ReadLn;
end.

EDIT
The above may return a date on Saturday or not, depending on the UNCLEAR_WHAT_YOU_R_ASKING conditional define.