Last day of each month and first day of each month (Delphi)

Procedure getmonthday (const adate: tdatetime;
VaR amonthfirst, amonthlast: tdatetime );
VaR
Year, month, day: word;
Begin
Decodedate (adate, year, month, day );
Amonthfirst: = encodedate (year, month, 1 );
If month + 1> 12 then
Amonthlast: = encodedate (Year + 1, 1, 1)-1
Else
Amonthlast: = encodedate (year, month + 1, 1)-1
End;

Procedure getmonthday (const adate: tdatetime;
VaR amonthfirst, amonthlast: tdatetime );
VaR
Year, month, day: word;
Begin
Decodedate (adate, year, month, day );
Amonthfirst: = encodedate (year, month, 1 );
Amonthlast: = encodedate (year, Inc (month), 1)-1
End;

First day of each month: encodedate (year, month, 1 );
Last day of each month: encodedate (year, Inc (month), 1)-1;

Day 1: strtodate ('2017-01-01 ')
Last day: strtodate ('2017-02-01 ')-1