[untested and because am lazy]

current_cam; //this is the current cam, default 0

function next_cam()
{
current_cam++; //go to next cam
current_cam%=9; //cycle between 9 cams
}

and in some other function or your main function, you can have:

on_c=next_cam;

now ofcourse you'll have to have each camera set to a number, for example:

if (current_cam==0)vec_set(camera.x,pos1.x); //set cam to position 1
if (current_cam==1)vec_set(camera.x,pos2.x); //so on and so forth

hope it helps... later