linear_search.dart

void main() {
  var list = List.generate(1000, (x) => x + 1);
  var result = linearSearch(list, 257);
  print('The result is: $result');
}

int? linearSearch(List<int> list, int target) {
  for (var i = 0; i < list.length; i++) {
    if(list[i] == target) {
      return i;
    }
  }
  return null;
}

Dartpad code: https://dartpad.dev/?id=5ab6837c9debd7b9243db7e4f648f90b