multiple selection list box values concat in a textbox

Hi All,

I have a client requirents and one of them is multiple selection list box control. When ever a user select any one or more value from multiple selection list box control, it should be concatenated in a textbox seperated by ",".

E.g.: user selected A B & C then the value should be concatenated in a textbox like A,B,C

Is there any formula to do this?

Thanks in Advance