Delphi uses Conditional compilation commands

Procedure tform1.btn1click (Sender: tobject );
Begin
{$ Define SS} (* defines a condition symbol. Once defined, the condition symbol is true *)
{$ Ifdef SS} (* determines the condition symbol, and compiles the source file if it is true *)
Showmessage ('ss has defined !! ');
Text: = 'ss has defined !! ';
Form1.color: = cllime;
{$ Else} (* used in combination with $ ifdef. If the $ ifdef condition is false, compile only a small part of the source file $ else *)
Showmessage ('ss has not defined !! ');
Text: = 'ss has not defined !! '
Form1.color: = clred;
{$ Endif} (* ends a condition segment starting with $ if *)


{$ Undef ss} (* revoking the previous conditional symbol definition *)

{$ Ifdef SS} (* because the SS definition has been revoked *)
Showmessage ('ss has defined !! ');
Text: = 'ss has defined !! ';
Form1.color: = cllime;
{$ Else}
Showmessage ('ss has not defined !! '); (* Therefore, the following statement is executed *)
Text: = 'ss has not defined !! ';
Form1.color: = clred;
{$ Endif}


End;