It is used in the code:
tt=Array{Int64}(undef,0)
but the following error is shown:
UndefVarError: undef not defined
would you please say why it happened? and is there any alternative for the code?

>Solution :

undef was introduced in Julia 0.7. If you are using a lower version, update Julia.

Or you can try tt=Array{Int64}(0). I don’t know whether this works in your system.