yes no menu cc

shell.run("clear")
print (" Panic Room Door control 0.2v")
print (" ----------------------------")
print (" [1] Open Door ")
print (" [2] Close Door ")
print (" [3] Exit ")
print (" [4] Shutdown Computer ")
input = read.io()
yes = "1"
no  = "2"
yo  = "3"
la  = "4"
if input == yes then
redstone.setOutput ("back", false)
shell.run("startup")
end
if input == no then
redstone.setOutput ("back", true)
shell.run("startup")
end
if input == yo then
shell.run("clear")
function mainmenu()
end
end
if input == la then
sleep(1)
os.shutdown()
end