Try this.
Program.adpt = new System.Data.SqlClient.SqlDataAdapter("select * from visitor_details", Program.con);
DataSet ds;
ds = new DataSet();
Program.adpt.Fill(ds);
if(ds.Tables[0].Rows.Cont > 0)
{
dataGridView1.AutoGenerateColumns = true;
dataGridView1.DataSource = ds.Tables[0];
}