char ch = e.KeyChar;
{
  if (!Char.IsDigit(ch) && ch != 8)
  {
  e.Handled = true;
  }
}

if (e.KeyChar == (char)Keys.Enter)
{
  decimal num = Decimal.Parse(TextBox1.Text); //  ottenere i migliaia
                TextBox1.Text = num.ToString("#,##0.00", CultureInfo.CurrentCulture.NumberFormat);
}
  if (TextBox1.Text.EndsWith("."))  //  ottenere i decimali
  {
     TextBox1.Text = TextBox1.Text.Substring(0, TextBox1.Text.Length - 1);
     TextBox1.AppendText(",");
  }

if ((e.KeyChar != (char)Keys.Back) && (!char.IsNumber(e.KeyChar.ToString(), 0)) && e.KeyChar != 44)
 e.Handled = true;
 if (e.KeyChar == 44 && TextBox1.Text.Split(',').Count() > 1)
 {
    e.Handled = true; 
  }
            
if (e.KeyChar == (char)Keys.Enter)
{
  TextBox2.Focus();
}

  private void TextBox1_KeyPress(object sender, KeyPressEventArgs e)
        {

            if (e.KeyChar == (char)Keys.Enter)
            {

                TextBox1.Text = TextBox1.Text.Replace(".", ",");
                decimal num = Decimal.Parse(TextBox1.Text); //  ottenere i migliaia
                TextBox1.Text = num.ToString("#,##0.00", CultureInfo.CurrentCulture.NumberFormat);
                TextBox2.Focus();
            }
        }

      private void TextBox1_KeyPress(object sender, KeyPressEventArgs e)
        {
            char ch = e.KeyChar;  //  Accetta solo numeri

            if (!Char.IsDigit(ch) && ch != 8)
            {
                e.Handled = true;
            }      
  
           if (ch == 44 || ch == 46)
            {
                e.Handled = false;
            }
         

            if (e.KeyChar == (char)Keys.Enter)
            {  

                TextBox1.Text = TextBox1.Text.Replace(".", ",");
                decimal num = Decimal.Parse(TextBox1.Text); //  ottenere i migliaia
                TextBox1.Text = num.ToString("#,##0.00", CultureInfo.CurrentCulture.NumberFormat);
              
            }
        }