clss01 var

class01var.dart

void main(){
  
  /// 1
  var data0 = 0;
  dynamic data1 = 1;
  int data2 = 2;
  final data3 = 3;
  const data4 = 4;
  
  
  /// 2
  data0 = 00;
  data1 = 11;
  data2 = 22;
  // data3 = 33; // err -> final
  // data4 = 44; // err -> const
  
  
  /// 3
  data0;
  data1;
  data2;
  data3;
  data4;
  
  
  /// 4
  var data5 = data0;
  dynamic data6 = data1;
  int data7 = data2;
  final data8 = data3;
  const data9 = data4;
  
  
  /// 5
  {
    int data10 = 10;
  }
  // data10; // err -> local
  
  
  /// 6
  int nData = 0;
  int? nData2 = 1;
  
  // nData = null; // err -> not null
  nData2 = null;
  
  nData2;
  
  // nData2 + 1; // warining -> nullable
  nData2! + 2; // safety
  
  (nData2 ?? 3) + 3; // best ! (1)
  nData2;
  
  (nData2 ??= 4) + 3; // best ! (2)
  nData2;
  
}