using list box in matlab gui

Question

i m doing a program  using list box and text box, using below coding

a=get(handles.listbox1,'value');
if(a==1)
set(handles.text1,'string','hello');
else if (a==2)
set(handles.text1,'string','hi');



but after writing this codes in callback function , receive one error (illegal use of reserved keyword"function").