Delphi Basics : Pred command

DelphiBasics

Pred
Function

Decrement an ordinal variable

System unit

function Pred(const Ordinal Value):Ordinal type;

Description

The Pred function decrements an ordinal value, and returns this value.

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 2 bytes if the pointer points to Words.

Notes

Pred is equivalent in performance to simple subtraction, or the Dec procedure.

Related commands

Dec		Decrement an ordinal variable
Inc		Increment an ordinal variable
Sqr		Gives the square of a number
Sqrt		Gives the square root of a number
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);
  Character := Pred(Character);
  ShowMessage('Character-1 : '+Character);

  // We can decrement numbers
  Number := 23;

  ShowMessage('Number : '+IntToStr(Number));
  Number := Pred(Number);
  ShowMessage('Number-1 : '+IntToStr(Number));

  // We can decrement enumerations
  Card := Clubs;

  ShowMessage('Card starts at Clubs');
  Card := Pred(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-1 : 22
  Card starts at Clubs
  Card is now Hearts