How to parse a 'String?' variable in Dart

Question

I am trying to parse an input with the type 'String?' into a double, but it is saying that -

The argument type 'String?' can't be assigned to the parameter type 'String'.

    stdout.write("Enter the first number - ");
    String? vari = stdin.readLineSync();
    var first = int.parse(vari);

score 0 · Answer 1 · answered Aug 21 '22 at 14:58

Change it to:

int? first = int.tryParse(vari.toString());

This is because String? is nullable, vs String.

.parse functions require non-nullable Strings.
tryParse returns an int if the string is parsable, and returns null if it can't be parsed. This is why I changed var first to int? first.
You can check afterwards if first is null or not. You can also perform this check before parsing it, and your code would look like this:

 String? vari = stdin.readLineSync();
 if (vari != null) var first = int.parse(vari);

This would work.

1 Answers1