Fill: SelectCommand.Connection property has not been initialized.

static string constring = ConfigurationManager.ConnectionStrings["cnstr"].ConnectionString;
         static SqlConnection con = new SqlConnection(constring);
        private void button1_Click(object sender, EventArgs e)
        {
            //con.Open();
           SqlCommand cmd = new SqlCommand("in_mem");
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.Parameters.AddWithValue("@sl_no",txtslno.Text); 
            cmd.Parameters.AddWithValue("@MemNo",txtmbm.Text);
            cmd.Parameters.AddWithValue("@name", txtnomname.Text);
            cmd.Parameters.AddWithValue("@deptno", txtdept.Text);
            cmd.Parameters.AddWithValue("@empno", txtemp.Text) ;
            cmd.Parameters.AddWithValue("@d_o_b", dateTimePicker1.Value) ;
            cmd.Parameters.AddWithValue("@d_o_m", dateTimePicker2.Value) ;
            cmd.Parameters.AddWithValue("@d_o_r",dateTimePicker3.Value) ;
            cmd.Parameters.AddWithValue("@nomi_name",txtnomname.Text) ;
            cmd.Parameters.AddWithValue("@relationship", txtrelation.Text) ;
            cmd.Parameters.AddWithValue("@address", txtaddr.Text);

            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();

            da.Fill(ds, "membership"); 
            //cmd.ExecuteNonQuery();

            //con.Close(); 
           MessageBox.Show("inserted succefully"); 
        }

 CREATE procedure in_mem(    
@sl_no numeric(18,0),    
@MemNo numeric(18,0),          
@name varchar(50),          
@deptno numeric(18,0),          
@empno numeric(18,0),          
@d_o_b date,          
@d_o_m date,          
@d_o_r date,          
@nomi_name varchar(50),          
@relationship varchar(50),          
@address varchar(50)          
)          
as           
begin           
insert into membership(sl_no,MemNo,name,deptno,empno,d_o_m,d_o_b,d_o_r,          
nomi_name,          
relationship,          
address          
)           
values(    
@sl_no,    
@MemNo,          
@name,          
@deptno,          
@empno,          
convert(varchar(10),@d_o_b,103),          
convert(varchar(10),@d_o_m,103),          
convert(varchar(10),@d_o_r,103),         
@nomi_name,          
@relationship,          
@address          
)          
end