[c#] How to get DataGridView cell value in messagebox?

How can I get DataGridView cell value to be written in the MessageBox in C#?

private void dataGridView1_CellClick(object sender, DataGridViewCellEventArgs e)
    {
           int rowIndex = e.RowIndex; // Get the order of the current row 
            DataGridViewRow row = dataGridView1.Rows[rowIndex];//Store the value of the current row in a variable
            MessageBox.Show(row.Cells[rowIndex].Value.ToString());//show message for current row
    }

MessageBox.Show(" Value at 0,0" + DataGridView1.Rows[0].Cells[0].Value );

   private void dataGridView1_CellEndEdit(object sender, DataGridViewCellEventArgs e)
    {
        MessageBox.Show(Convert.ToString(dataGridView1.CurrentCell.Value));
    }

a bit late but hope it helps

private void dataGridView1_CellClick(object sender, DataGridViewCellEventArgs e)
{
    if (dataGridView1.Rows[e.RowIndex].Cells[e.ColumnIndex].Value != null)
    {
       MessageBox.Show(dataGridView1.Rows[e.RowIndex].Cells[e.ColumnIndex].Value.ToString());
    }
}

I added this to the Button of a datagrid to get the values of the cells in the row that the user is clicking:

string DGCell = dataGridView1.Rows[e.RowIndex].Cells[X].Value.ToString();

where X is the cell you want to check. Datagrid column count starts at 1 not 0 in my case. Not sure if it is default of a datagrid or because I am using SQL to populate the info.

      try
        {

            for (int rows = 0; rows < dataGridView1.Rows.Count; rows++)
            {

                for (int col = 0; col < dataGridView1.Rows[rows].Cells.Count; col++)
                {
                    s1 = dataGridView1.Rows[0].Cells[0].Value.ToString();
                    label20.Text = s1;
                }
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show("try again"+ex);
        }

Sum all cells

        double X=0;
        if (datagrid.Rows.Count-1 > 0)
        {
           for(int i = 0; i < datagrid.Rows.Count-1; i++)
            {
               for(int j = 0; j < datagrid.Rows.Count-1; j++)
               {
                  X+=Convert.ToDouble(datagrid.Rows[i].Cells[j].Value.ToString());
               }
            } 
        }