How to call a dialog from a mainwindow

[luiz4um]

I want to build an interface and I need to link a pushbutton in a mainwindow with a dialog. Both were made in Qt Designer. I tried some answers that I saw in others thread but I think it doesn't help me. So, here it goes my codes:
Mainwindow: telainicial (.h/.cpp)
Dialog: simples (.h/.cpp)

telainicial.h

#ifndef TELAINICIAL_H
#define TELAINICIAL_H
 
#include <QMainWindow>
#include "ui_telainicial.h"
 
class telainicial : public QMainWindow, public Ui::telainicial {
    Q_OBJECT
public:
    telainicial(QWidget *parent = 0);
private slots:
    void telasimples();
};
 
#endif // TELAINICIAL_H

#ifndef TELAINICIAL_H
#define TELAINICIAL_H

#include <QMainWindow>
#include "ui_telainicial.h"

class telainicial : public QMainWindow, public Ui::telainicial {
    Q_OBJECT
public:
    telainicial(QWidget *parent = 0);
private slots:
    void telasimples();
};

#endif // TELAINICIAL_H

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telainicial.cpp

#include <QtGui>
#include "telainicial.h"
#include "simples.h"
 
telainicial::telainicial(QWidget *parent) :
    QMainWindow(parent)
 
{
    setupUi(this);
 
    connect(lentesimplesButton, SIGNAL(clicked()), this, SLOT(telasimples()));
 
}
 
void telainicial::telasimples(){
 
    //code goes here
 
 };

#include <QtGui>
#include "telainicial.h"
#include "simples.h"

telainicial::telainicial(QWidget *parent) :
    QMainWindow(parent)

{
    setupUi(this);

    connect(lentesimplesButton, SIGNAL(clicked()), this, SLOT(telasimples()));

}

void telainicial::telasimples(){

    //code goes here

 };

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simples.h

#ifndef SIMPLES_H
#define SIMPLES_H
 
#include <QDialog>
#include "ui_simples.h"
 
class simples : public QDialog, public Ui::simples {
    Q_OBJECT
 
public:
    simples(QWidget *parent = 0);
 
};
 
#endif

#ifndef SIMPLES_H
#define SIMPLES_H

#include <QDialog>
#include "ui_simples.h"

class simples : public QDialog, public Ui::simples {
    Q_OBJECT

public:
    simples(QWidget *parent = 0);

};

#endif

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simples.cpp

#include "simples.h"
#include <QtGui>
 
simples::simples(QWidget *parent) :
    QDialog(parent)
 
{
    setupUi(this);
}

#include "simples.h"
#include <QtGui>

simples::simples(QWidget *parent) :
    QDialog(parent)

{
    setupUi(this);
}

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The mains files are similiar like this:

#include <QtGui/QApplication>
#include "telainicial.h"
 
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    telainicial mainwindow;
    mainwindow.show();
    return app.exec();
}

#include <QtGui/QApplication>
#include "telainicial.h"

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    telainicial mainwindow;
    mainwindow.show();
    return app.exec();
}

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Can somebody help me?