function Dec(var X: Ordinal; [ N: Integer]): Integer; overload; function Dec(var X: Ordinal; [ N: Integer]): Integer; overload;
Decrements a variable by 1 or N.
In Object Pascal code, Dec subtracts one or N from a variable.
X is a variable of an ordinal type (including Int64), or a pointer type if the extended syntax is enabled.
N is an integer-type expression.
X decrements by 1, or by N if N is specified; that is, Dec(X) corresponds to the statement X := X - 1, and Dec(X,N) corresponds to the statement X := X - N. On some platforms, Dec may generate optimized code, especially useful in tight loops.
If X is a pointer type, it decrements X by N times the size of the type pointed to. Thus, given:
type PMyType = ^TMyType;
var P: PMyType;
the statement Dec(P) decrements P by SizeOf(TMyType).
Warning: Do not use Dec on ordinal-type properties if the property uses a write procedure.