hey dude!
i have a solution for your question! i hope help you ...
here we have a foreach to check any cell of selected rows of datagridview .
an int variable will count cells untill foreach arrive to last cell!
we have an indexer into DataGridViewRow Class that return value of cells which counter specified!
int counter=0;
foreach (DataGridViewRow dr in dataGridView1.SelectedRows)
{
richtextbox.Text +=dr.Cells[counter].Value.ToString();
}
hope help you!