Dynamic arrays

var A: array of Integer; has no fixed size. Allocate it with SetLength(A, 10). Indexes run from 0 to High(A).

Dynamic arrays are reference-counted. B := A shares the data, so a write through one shows up in the other until one is resized. Use B := Copy(A) for an independent copy.

Free Pascal 3.2 adds Insert(Value, A, Index), Delete(A, Index, Count), Concat, and array literals such as A := [1, 2, 3].

Growing one element at a time (SetLength(A, Length(A) + 1)) is O(n) per call, because each resize can copy the whole array. Grow the capacity in big steps, such as doubling it, or use TList.

Arrays of arrays (array of array of Integer) can be jagged.

program DynArrays;
{$mode objfpc}{$H+}
var
  A, B, C: array of Integer;
  Jag: array of array of Integer;
  I: Integer;
begin
  A := [5, 3, 8];
  SetLength(A, 5);
  A[3] := 1; A[4] := 9;
  writeln(Length(A), ' ', High(A));
  B := A;
  C := Copy(A);
  A[0] := 100;
  writeln(B[0], ' ', C[0]);
  Insert(42, C, 1);
  Delete(C, 0, 1);
  for I in C do write(I, ' ');
  writeln;
  SetLength(Jag, 3);
  for I := 0 to 2 do SetLength(Jag[I], I + 1);
  writeln(Length(Jag[0]), Length(Jag[2]));
end.