I can not use int j = int32.parse(readline()); in visual studio 2019?

No, because it doesn't know what "ReadLine" method you want to use.
If you are trying to read what the user is typing, then you want the COnsole:

int j = Int32.Parse(Console.ReadLine());

If you are trying to read from a file then you need to specify the Stream that is attached to the file:

int j = Int32.Parse(MyFileStream.ReadLine());

But eitehr way, I'd strongly suggest you use TryParse instead of Parse:

int j;
string input = Console.ReadLine();
if (!Int32.TryParse(input, out j))
   {
   ... report or log a problem here: the input line was not a valid integer ...
   return;
   }

As users are very prone to mistyping and it's "unfriendly" to just crash your app when they do that.
TryParse returns a true / false to say "It worked / it failed" instead of throwing an exception and crashing your app.