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

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

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

  ShowMessage('Character : '+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');
  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');
Show 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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