DelphiBasics
Dec
Procedure
Decrement an ordinal variable System unit
1  procedure Dec ( var Variable : Ordinal variable ) ;
2  procedure Dec ( var Variable : Ordinal variable; Count : Integer ) ;
Description
The Dec procedure decrements the ordinal Variable parameter passed to it.
 
You can decrement :
 
Characters 
Non-floating number types 
Enumeration types 
Pointers 

 
The decrement is by the base size of the unit. For example, decrementing a Pointer will be by 4 bytes if the pointer points to Words.
 
Version 1 of Inc decrements by 1 unit.
 
Version 2 of Inc decrements by Count units.
 
Notes
Dec is equivalent in performance to simple subtraction, or the Pred procedure.

Count can be negative.
Related commands
Inc Increment an ordinal variable
Pred Decrement an ordinal variable
Sqr Gives the square of a number
Sqrt Gives the square root of a number
Succ Increment an ordinal variable
Succ Increment an ordinal variable
Sum Return the sum of an array of floating point values
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Example code : Decrementing characters, numbers and enumerations
// Full Unit code.
// -----------------------------------------------------------
// You must store this code in a unit called Unit1 with a form
// called Form1 that has an OnCreate event called FormCreate.
 
unit Unit1;
 
interface
 
uses
  // The System unit does not need to be defined
  SysUtils,
  Forms, Dialogs;
 
type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
  end;
 
var
  
Form1: TForm1;
 
implementation
{$R *.dfm} // Include form definitions
 
procedure TForm1.FormCreate(Sender: TObject);

type
  TSuit = (Hearts, Clubs, Diamonds, Spades);
var
  Character : char;
  Number    : Integer;
  Card      : TSuit;

begin
  // We can decrement characters
  Character := 'B';

  ShowMessage('Character : '+Character);
  Dec(Character);
  ShowMessage('Character-1 : '+Character);

  // We can decrement numbers
  Number := 23;

  ShowMessage('Number : '+IntToStr(Number));
  Dec(Number, 5);
  ShowMessage('Number-5 : '+IntToStr(Number));

  // We can decrement enumerations
  Card := Clubs;

  ShowMessage('Card starts at Clubs');
  Dec(Card);
  if Card = Hearts then ShowMessage('Card is now Hearts');
  if Card = Clubs then ShowMessage('Card is now Clubs');
  if Card = Diamonds then ShowMessage('Card is now Diamonds');
  if Card = Spades then ShowMessage('Card is now Spades');
end;
 
end.
Hide full unit code
   Character : B
   Character-1 : A
   Number : 23
   Number-5 : 18
   Card starts at Clubs
   Card is now Hearts
 
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