local tb={1,2,3,4}


for key,value in pairs(tb) do
    while(true) do
        if 3 == key then
            print("3")
            return
        else
           print("break")
           break
        end
   end
   print("out while")
end
print("out for")

local aa=""

if aa then
        print("aa is ,",aa)
else
        print("aa is nil")
end

#结果 aa is ,