Check if variable exists and edit problems

Hi! I'm doing little spam on foum, sry for that :D/>

How can I check if variable isnt nil ?

Here is my code: http://pastebin.com/07szXe0i

I'm saying about Tank() function.
I tried if variable == nil but it doesnt work

The second problem is terminating program
When i am in tank mode ($$tank show) and i terminate program, i cant edit it. It says: edit:60: attempt to call nil
I have to reboot PC then.

EDIT: I need checking var because i saw, when tank is empty, his liquid amount is nil, so table[1].amount is nil and program crashes

if variable then
  --not nil
else
  --nil
end

AS for your other problem, you're overwriting the global table functions with this line

    table = tank_p.getTankInfo("unknown")

the word table is already in use by the global environment, to store all table functions. Either make it a local definition or change the name of your table variable.

Thank you! Is it possible to do:

if variable then
–nil
end

?

i tried ~variable but it doesnt work

Ok, i've got it, just use not var :D/>

Well, if variable then checks if it is not nil and not false. If your variable may be false do: if variable ~= nil then

OczkoSX was saying he figured out "if not variable then" does the trick.

That still gives you the same problem, if it's false or nil then it not var will be true

I said I know, just have to use

if not var then