Decrements a variable.
procedure Dec(var X[ ; N: Longint]);
Windows, Real, Protected
X is an ordinal-type variable or a variable of type PChar if the extended syntax is enabled, and N is an integer-type expression. X is decremented by 1, or by N if N is specified; that is, Dec(X) corresponds to X := X - 1, and Dec(X, N) corresponds to X := X - N.
Dec generates optimized code and is especially useful in a tight loop.