How to insert null in datetime type column in sql server

Question

I have a table in which there are some datetime type columns. I use a stored procedure to insert values into the table. In the stored procedure I have variables that accept null

Answer 1

if (//some condition)   
{
   cmd.Parameters.AddWithValue("@dateofBirth", txtdob.text);
}
else 
{ 
   cmd.Parameters.AddWithValue("@dateofBirth", DBNull.Value); 
}