c# - How to implement validation for negative values -

i working on code snippet

  private void calculatebutton_click(object sender, eventargs e)     {         int amount;         if (int.tryparse(amounttextbox.text, out amount))         {             wantedtextbox.text = currency_exchange.exchangecurrency((currencies)currencycombobox.selectedindex, (currencies)wantedcurrencycombobox.selectedindex, amount).tostring("0.00");                             wantedcurrencylable.text = ((currencies)wantedcurrencycombobox.selectedindex).tostring();         }          else {             messagebox.show("invalid amount");         }       } 

and realized way late should put in validation negative numbers. way i've set code makes difficult. how this?

store value of tryparse result, check amount in same if statement, so:

boolean parseresult = int.tryparse(amounttextbox.text, out amount)  if (parseresult && amount >= 0) {     //.... } else {     messagebox.show("invalid amount"); }