Delphi Basics : Dec command

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

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;

Show full unit code

  Character : B
  Character-1 : A
  Number : 23
  Number-5 : 18
  Card starts at Clubs
  Card is now Hearts