Приращение количества не работает с буквами только с числами

Some help
 
In line 10 setup IsLetterOrDigit..
 
When add some value in datagrid
 
 Line 34-39 have problem...
 
Every time add new row, if put number  it ok kolicina (quantity go up +1), if is bar code type vm1403 add new row...not kolicina (quantity) +1...why? Some help?

    int cqty = Convert.ToInt32(row.Cells["kolicina"].Value) + 1;  
      
                              if (textBox1.Text == row.Cells["bar_kod"].Value.ToString())  
                              {  
                                  row.Cells["kolicina"].Value = cqty;  

private void prijavaAction()  
      {  
          PullData();  
                
                
          int sno = dataGridView1.Rows.Count + 1;  
  
          SqlConnection con2 = new SqlConnection(con);  
  
          if (textBox1.Text.All(char.IsLetterOrDigit))  
  
          {  
              string queryString = "select [bar_kod], [naziv], [cijena_sa_porezom] from dbo.roba_usluge WHERE [bar_kod] = '" + textBox1.Text + "'";// pronaci artikl u bazi                
              using (SqlConnection connection = new SqlConnection(con))  
              {  
                  SqlCommand command = new SqlCommand(queryString, connection);  
                  connection.Open();  
                  SqlDataReader reader = command.ExecuteReader();  
  
  ///////////////////////////////////////////

here is error
                  var itemAndPrice = textBox1.Text;  
  
                  var SingleRow = (from Rows in dataGridView1.Rows.Cast<DataGridViewRow>() where !Rows.IsNewRow && Rows.Cells["bar_kod"].Value.ToString().ToUpper() == textBox1.Text.ToUpper() select Rows).FirstOrDefault();  
  
  
                  if (reader.Read())  
                  {  
  
                      bool barcodeexist = false;  
                      foreach (DataGridViewRow row in dataGridView1.Rows)  
                      {  
                          int cqty = Convert.ToInt32(row.Cells["kolicina"].Value) + 1;  
  
                          if (textBox1.Text == row.Cells["bar_kod"].Value.ToString())  
                          {  
                              row.Cells["kolicina"].Value = cqty;  
   ///////////////////////////////////////////


                              foreach (DataGridViewRow g1 in dataGridView1.Rows)  
                              {  
  
  
                                  g1.Cells["ukupno"].Value = (Convert.ToDouble(g1.Cells["kolicina"].Value) * Convert.ToDouble(g1.Cells["cijena"].Value)).ToString("0.00");  
  
                              }