type
  TMyArr = array of Integer;
...
function MyFunc (c, x: Integer): TMyArr;
...
implementation
...
function MyFunc (c, x: Integer): TMyArr;
var
  i: Integer;
begin
  SetLength (Result, c);
  for i := 0 to c-1 do Result [i] := x;
end;
...
 
procedure TForm1.Button3Click(Sender: TObject);
var
  a: TMyArr;
...
begin
  a := MyFunc (3, 5);
...
end;