"using" statement vs. curly brackets

Question

I wonder why we do use using statement in C#. I looked it up, and found that it is used for executing the statements and then cleaning up the objects. So my question: Isn't it the same thing if we open and close curly brackets( { } ) to define a scope?

Using statement:

using (SqlConnection conn = new SqlConnection(connString)) {
     SqlCommand cmd = conn.CreateCommand();
     cmd.CommandText = "SELECT * FROM Customers";
     conn.Open();
     using (SqlDataReader dr = cmd.ExecuteReader()) {
          while (dr.Read()) 
          // Do Something...
     }
}

Curly Brackets:

{
     SqlConnection conn = new SqlConnection(connString);
     SqlCommand cmd = conn.CreateCommand();
     cmd.CommandText = "SELECT * FROM Customers";
     conn.Open();
     {
          SqlDataReader dr = cmd.ExecuteReader();
          while (dr.Read()) 
          // Do Something...
     }
}

Are there any significant differences between two methods?

Answer 1

Well, using (which is legal if and only if the class implements IDisposable interface)

using (SqlConnection conn = new SqlConnection(connString)) {
  // Some Code
  ...
}

is equal to this block of code

SqlConnection conn = null;

try {
  SqlConnection conn = new SqlConnection(connString);

  // Some Code
  ...
}
finally {
  if (!Object.ReferenceEquals(null, conn))
    conn.Dispose();
}

C# doesn't have the same behavior as C++ does, so do not use {...} pattern in C# as you do in C++:

{
  SqlConnection conn = new SqlConnection(connString);
  ...
  // Here at {...} block exit system's behavior is quite different:
  //
  // C++: conn destructor will be called, 
  // resources (db connection) will be safely freed
  //
  // C#:  nothing will have happened! 
  // Sometimes later on (if only!) GC (garbage collector) 
  // will collect conn istance and free resources (db connection). 
  // So, in case of C#, we have a resource leak 
}