How to check all the row of the datagrid

Here What I have coded for It

in ur case its 1st Column Use Cell[0]

private void chkCheckAll_CheckedChanged(object sender, EventArgs e)
        {
            if (chkCheckAll.Checked == true)
            {

                foreach (DataGridViewRow dr in dataGridView1.Rows)
                {
                    dr.Cells[1].Value = true;
                }

            }

            else if(chkCheckAll.Checked == false )
            {

                foreach (DataGridViewRow dr in dataGridView1.Rows)
                {
                    dr.Cells[1].Value = false ;
                }
            }

            }

Here is Source Code file if you Not Getting it By code
http://www.mediafire.com/?sharekey=2e9d884c2476e3fad2db6fb9a8902bda

Happy Coding :)