How to determine whether the left mouse button or right button is pressed in the onmousedown event

For example, in the onmousedown, there is a parameter is button, he represents the mouse button is caused by the event, while the shift shows the state of the keys at this time (not only the left button, right button, and Alt,ctrl keyboard keys, Specifically, you can see the definition of tshiftstate, in CLASSES.HPP).
The code is as follows, if L is displayed, the left button is pressed, the R is displayed, the right button is pressed and all the display is pressed.
void __fastcall Tform1::formmousedown (tobject *sender, Tmousebutton Button,
Tshiftstate Shift, int X, int Y)
{
Ansistring sbuttonstate;
if (Shift.contains (Ssleft))
{
Sbuttonstate + = "L";
}
if (Shift.contains (ssright))
{
Sbuttonstate + = "R";
}

Caption = sbuttonstate;
}