Don't use fixed list, use an array of possible choices and keep a corollary variable of those already taken so those aren't ever shown as available to the next user.
A menu of such long list isn't really a particularly friendly UI, but that would be the way to code it as a first learning coding experience.
ADDENDUM
A small example of the idea; will need to factor out the "what to do" stuff rather than try to keep all inline as is below, but illustrates the idea of keeping track of which vehicles are in inventory.
Obviously need a "check in" function that does the reverse that would, of course, use pool(~ix) to present those from which to select.
NB: the addition of an 'Exit' button first for convenience and being a little neater than just closing the window; there's some bookkeeping associated with that to keep straight which car is actually the one associated with the menu.
N=4;
pool=[1:N].'; % available car pool
go=true; % flag to run selection
n=0; % initialize number out
ix=true(1,N); % those available
while go
cars=cellstr(['Exit';num2str(pool(ix),'Car%0d')]);
c=menu('Select a car',cars); % ask for selection correct w/ Exit==1
if c<=1
go=false; % bail on exit or quit
else
ix(pool(c-1))=false; % make this one unavailable
n=n+1; % count number in use
fprintf('Chose car: %s. In use: %d\n', cars{c}, n)
if n==N
disp('Inventory Depleted. Bye')
go=false;
end
end
end
Also NB: menu is deprecated; it is suggested to use dialog instead and as noted before, something more user-friendly than 40 pushbuttons in a long column would be the obvious choice instead if coding "in anger" and not just as learning exercise.
