Count the number of Mondays between two given dates

Problem/Question/Abstract:

How to count the number of Mondays between two given dates

Answer:

Solve 1:

function NumMondays(dt1, dt2: TDateTime): integer;
var
  Date1, Date2, DateSpan: integer;
  Weekday1, DaysInStub: integer;
  MondayInStub: Boolean;
begin
  {Make sure date 1 is smaller than date 2}
  Date1 := MinIntValue([Trunc(dt1), Trunc(dt2)]);
  Date2 := MaxIntValue([Trunc(dt1), Trunc(dt2)]);
  {First approximation: complete weeks}
  DateSpan := Date2 - Date1 + 1;
  result := DateSpan div 7;
  {Now check if there's a Monday in the stub}
  MondayInStub := false;
  DaysInStub := DateSpan mod 7;
  Weekday1 := DayOfWeek(Date1);
  case Weekday1 of
    {Sunday}
    1: MondayInStub := DaysInStub > 0;
    {Monday}
    2: MondayInStub := true; {Starts and ends with Monday}
    {Sunday}
    3..7: MondayInStub := (Weekday1 + DaysInStub > 9 {2+7});
  end;
  if MondayInStub then
    inc(result);
end;


Solve 2:

Something like this should do the trick. I included the variable setup and display of results from my little test so that it will be obvious what I did.

procedure TForm1.Button1Click(Sender: TObject);
var
  cnt: integer;
  StartDate, EndDate: TDate;
begin
  cnt := 0;
  StartDate := StrToDate('4/21/2003');
  EndDate := StrToDate('5/30/2003');
  {Actual Monday counting}
  repeat
    if DayOfWeek(StartDate) = 2 then {2 = Monday (Sun = 1 .. Sat = 7) }
      inc(cnt);
    StartDate := StartDate + 1;
  until
    StartDate = EndDate;
  label1.Caption := IntToStr(cnt);
end;