Newline Inside a String To Be Shown At a TMemoBox

The solution is to use #13#10 or better as Sertac suggested sLineBreak.

FullMemo := txtFistMemo.Text + #13#10 + txtDetails.Text;
FullMemo := txtFistMemo.Text + sLineBreak + txtDetails.Text;

A more platform independent solution would be TStringList.

var
  Strings: TStrings;
begin
  Strings := TStringList.Create;
  try
    Strings.Assign(txtFirstMemo.Lines); // Assuming you use a TMemo
    Strings.AddStrings(txtDetails.Lines);
    FullMemo := Strings.Text;
  finally
    Strings.Free;
  end;
end;

To Add an empty newline you can use:

Strings.Add('');

Use

FullMemo := txtFistMemo.Text + #13#10 + txtDetails.Text