Textbox entry giving errors in c# : **I have 4 text boxes. In first textbox just i am doubleclicking and opening child form.there i am displaying some names and values. I am selecting one name in that form and that name is coming to first form first text box and next text box value is coming. next I want to take input using third text box and do some caliculations, display result in fourth textbox(readonly one).but it is giving some error.what I made mistake.
here is my code
Below code I wrote to take values from child form**

  

        private void dataGridView1_CellDoubleClick(object sender, DataGridViewCellEventArgs e)
            {
                //MessageBox.Show(dataGridView1.CurrentRow.Cells[3].Value.ToString());
                
                Form8.code = dataGridView1.CurrentRow.Cells[0].Value.ToString();
                
                Form8.name = dataGridView1.CurrentRow.Cells[1].Value.ToString();
                Form8.fiel= dataGridView1.CurrentRow.Cells[6].Value.ToString();
                Form8.measure= dataGridView1.CurrentRow.Cells[2].Value.ToString();
    
    below Code of my main form to store that values 
         boxname.Text = name;
                    if (boxname.Text == "")
                    {
                        MessageBox.Show("Empty Name");
                    }
                    else
                    {
                        //boxname.Text = name;
    
                        boxbprice.Text = fiel;
                        double qty=Convert.ToDouble(boxqty.Text);//taking quanty  input and storing that a double datatype variable.
                                  
                      }

> where I did mistake.it is giving some error 
> "input String was not in a currect format"
