I'm currently studying wxWidgets programming, and everything's going just fine... Except for one part, that is. The project I'm working on is a Celsius to Fahrenheit converter. So far, I have three files: CelsiusFahrenheit.cpp, Utilitarios.h, Utilitarios.cpp, the first of which contains the main program. Here's the code:

CelsiusFahrenheit.cpp

Code:
#define CELSIUS_BUTTON_ID 1
#define FAHRENHEIT_BUTTON_ID 2
#include "wx/wx.h"

#include "Utilitarios.h"
#include <string>
using namespace std;

class CelsiusFahrenheit: public wxApp {
  public:
    //Variaveis globais
    wxTextCtrl* celsius_text;
    wxTextCtrl* fahrenheit_text;
    //Metodo OnInit, iniciador da aplicacao
    bool OnInit() {
      //Inicializa a janela
      wxSize* tamanho_janela = new wxSize(640,480);
      wxString* titulo = new wxString("Conversor Celsius-Fahrenheit-Celsius");
      wxFrame* janela = new wxFrame(NULL, -1, *titulo, wxDefaultPosition, *tamanho_janela);
      //Inicializa os controlos de texto
      int celsius_text_x = 0;
      int celsius_text_y = 0;
      int fahrenheit_text_x = celsius_text_x;
      int fahrenheit_text_y = celsius_text_y + 50;
      wxPoint* posicao_celsius_text = new wxPoint(celsius_text_x,celsius_text_y);
      wxPoint* posicao_fahrenheit_text = new wxPoint(fahrenheit_text_x,fahrenheit_text_y);
      wxSize* tamanho_texto = new wxSize(200, 25);
      celsius_text = new wxTextCtrl(janela, -1, "", *posicao_celsius_text, *tamanho_texto);
      fahrenheit_text = new wxTextCtrl(janela, -1, "", *posicao_fahrenheit_text, *tamanho_texto);
      *celsius_text << "Valor em graus Celsius";
      *fahrenheit_text << "Valor em graus Fahrenheit";
      //Inicializa os botoes
      wxSize* tamanho_botoes = new wxSize(200, 25);
      wxPoint* posicao_celsius_button = new wxPoint(celsius_text_x + tamanho_texto->GetWidth(),celsius_text_y);
      wxPoint* posicao_fahrenheit_button = new wxPoint(fahrenheit_text_x + tamanho_texto->GetWidth(),fahrenheit_text_y);
      wxButton* celsius_button = new wxButton(janela, CELSIUS_BUTTON_ID, "", *posicao_celsius_button, *tamanho_botoes);
      wxButton* fahrenheit_button = new wxButton(janela, FAHRENHEIT_BUTTON_ID, "", *posicao_fahrenheit_button, *tamanho_botoes);
      celsius_button->SetLabel("Converter Celsius para Fahrenheit");
      fahrenheit_button->SetLabel("Converter Fahrenheit para Celsius");
      janela->Show(true);
      return true;
    }
    //Tratadores de eventos
    void OnCelsiusClick(wxCommandEvent& event) {
      string s(celsius_text->GetValue());
      int i = stringToInteger(s);
      exit(0);
    }
    void OnFahrenheitClick(wxCommandEvent& event) {
      exit(0);
    }
    //Instrucao necessaria para que esta classe possa tratar eventos
    DECLARE_EVENT_TABLE()
};

//Eventos da classe CelsiusFahrenheit
BEGIN_EVENT_TABLE(CelsiusFahrenheit, wxApp)
 EVT_BUTTON(CELSIUS_BUTTON_ID, CelsiusFahrenheit::OnCelsiusClick)
 EVT_BUTTON(FAHRENHEIT_BUTTON_ID, CelsiusFahrenheit::OnFahrenheitClick)
END_EVENT_TABLE()
//Iniciar a aplicacao
IMPLEMENT_APP(CelsiusFahrenheit)
Utilitarios.h

Code:
#ifndef _UTILITARIOS_H_
#define _UTILITARIOS_H_
class Utilitarios {
  public:
    int stringToInteger(string& s);
};
#endif
Utilitarios.cpp

Code:
#include "Utilitarios.h"
#include <sstream>
#include <string>
using namespace std;

int Utilitarios::stringToInteger(string& s) {
  stringstream temp;
  temp << s;
  int i = 0;
  if (temp >> i) {
    return i;
  }
  else {
    throw "Number format exception!";
  }
}
And the problem is the following compilation error:

Line 5 - Utilitarios.h - expected `;' before '(' token

What exactly am I doing wrong? Thank you in advance.