dart_basics/lib/basic_part2.dart

void basic_variables() {

  print("\nDart Variables:");
  var name = "Bobson";
  // name = 123;
  // Error: A value of type 'int' can't be assigned to a variable of type 'String'.
  print(name);
  
  dynamic myName = "Bobson";
  print(myName);
  myName = 123;
  print(myName);

  // var list = [
  //   1,
  //   "2",
  //   3.0,
  //   true,
  //   () {},
  //   #symbol,
  //   Runes("123"),
  //   [1, 2, 3],
  //   {"A": 4}
  // ];

  int lineCount;
  assert(lineCount == null); // default value is null
}

void basic_control_flow() {
  print("\nDart Control Flow:");

  int number = -5;
  // If Else
  if (number > 0) {
    print("$number 大於 0");
  } else if (number < 0) {
    print("$number 小於 0");
  } else {
    print("$number 等於 0");
  }

  // Switch
  switch (number > 0) {
    case true:
      print("$number 大於 0");
      break;
    default:
      print("$number 小於等於 0");
  }

  DownloadState downloadState = DownloadState.done;

  switch (downloadState) {
    case DownloadState.none:
      print("尚未下載");
      break;
    case DownloadState.downloading:
      print("下載中");
      break;
    case DownloadState.done:
      print("下載完成");
      break;
    case DownloadState.error:
      print("下載失敗");
      break;
    default:
      throw Exception("異常狀態");
  }

  // For loop
  var collection = [];
  for (var i = 0; i < 3; i++) {
    collection.add(i);
  }
  print(collection);

  collection.forEach((i) => print("${i+1}"));
  print(collection.map((i) => i+1));

  for (var c in collection) {
    print(c);
  }

  // While
  int count = 0;
  while (count < 5) {
    count += 1;
  }
  print(count);

  do {
    count += 5;
    print("count 加一次 5");
  } while (count < 14);
  print(count);

  // Break Continue
  count = 0;
  while (count < 5) {
    if (count == 4) {
      count += 3;
      continue;
    }
    // continue 會忽略這行，直接進入下一個迴圈

    count += 1;
  }
  print(count);

  do {
    count += 5;
    print("count 加一次 5");
    if (count % 2 == 0) break;
  } while (count < 14);
  print(count);
}

enum DownloadState {
  none,
  downloading,
  done,
  error
}