Constants

A constant is an identifier that marks a value that cannot change. The normal decimal notation is used for numbers that are integer or real constants. A hexadecimal integer constant uses a dollar sign as a prefix. It is also possible to use the engineering notation, where an exponent follows the E or e character.

A character string is a sequence of zero or more characters written in one line in the program and enclosed within apostrophes. A character string with nothing between the apostrophes is called a null string. Two sequential apostrophes in a character string denote a single apostrophe character.

For example, a string constant would print out as just Paweł's computer, as shown in the following program:

const 
  s = 'Paweł''s computer'; 

Object Pascal allows the use of constant expressions. The compiler evaluates them at compile time without actually executing the program.

Object Pascal makes it possible to embed control characters in character strings. The # character followed by an unsigned integer in the range of 0 to 255 means a character of the corresponding ASCII value. A useful example of this capability is embedding a newline character in a string constant, so it is displayed in multiple lines. For example, check out the following code snippet:

const EL = #13; 
 
procedure TForm1.ButtonMultilineClick(Sender: TObject); 
begin 
  ShowMessage('Welcome!' + EL + 'Good morning!'); 
end; 

Embedding the new ASCII 13 newline control character displays the message in two lines. For readability, the actual newline character is defined as a constant.