GOT SOLUTION here it is....
private void button3_Click(object sender, EventArgs e)
{
var selectedidlist = new List<string>();
for (var rownum = 0; rownum < dataGridView1.Rows.Count; rownum++)
{
if (dataGridView1.Rows[rownum].Cells["Column1"].Value!=null && ((bool)(dataGridView1.Rows[rownum].Cells["Column1"]).Value))
{
selectedidlist.Add(dataGridView1.Rows[rownum].Cells["USN"].Value.ToString());
}
}
if (selectedidlist.Count > 0)
{
var selectedListString = selectedidlist.Aggregate((current, next) => current + ", " + next);
String str = "delete from T_BOOK_ISSUE_TABLE where USN in (@search)";
SqlCommand xp = new SqlCommand(str, vid);
xp.Parameters.Add("@search", SqlDbType.NVarChar).Value = selectedListString;
vid.Open();
xp.ExecuteNonQuery();
vid.Close();
Delete_Load(null, null);
}