Calling a function

hello

here is my prob :

on frame 1 : I define a function
exemple : function exemple(){
a=1;
}//end function

on frame 2 : line0 :exemple()
line1 : trace(a);

=> but there is no trace of a. the function has not been called

but if I add a button with on release exemple(), the function exemple has been called

is this normal ? how can I call and execute a function without calling it trough a button.

thanks for your help !