How to display my application gui

I have made an application and it has a Qtableview,four form fields of Qlinedit,Qgridlayout and five buttons.The application builds without any errors but exits when i try to run it with the windows error message : "smith.exe has encountered a problem and needs to close. We are sorry for the inconvenience.".

Other examples i have run correctly.

Here is the code.

smith.h

Code:

#ifndef SMITH_H
#define SMITH_H
 
#include <QWidget>
 
QT_BEGIN_NAMESPACE
class QPushButton;
class QLabel;
class QLineEdit;
class QTableView;
class QDataWidgetMapper;
class QSqlTableModel;
QT_END_NAMESPACE
 
class smith : public QWidget
{
    Q_OBJECT
 
public:
   smith(QWidget *parent = 0);
 
private:
 
 void setupModel();
 
 QDataWidgetMapper *mapper;
 QSqlTableModel *tableModel;
 QTableView *tableView;
 QLabel *fnLabel;
 QLabel *lnLabel;
 QLabel *countryLabel;
 QLabel *cityLabel;
 QLineEdit *fEdit;
 QLineEdit *lnEdit;
 QLineEdit *cEdit;
 QLineEdit *cityEdit;
 QPushButton *newButton;
 QPushButton *nextButton;
 QPushButton *previousButton;
 QPushButton *saveButton;
 QPushButton *deleteButton;
 
private slots:
    void on_deleteButton_clicked();
    void on_saveButton_clicked();
    void on_newButton_clicked();
};
 
#endif // SMITH_H

smith.cpp

Code:

#include <QtGui>
#include <QtSql>
#include "smith.h"
 
smith::smith(QWidget *parent) :
    QWidget(parent)
{
 
    setupModel();
 
    QLabel *fnLabel = new QLabel(tr("First Name:"));
    fEdit = new QLineEdit;
    fEdit->setReadOnly(true);
 
    QLabel *lnLabel = new QLabel(tr("Last Name:"));
    lnEdit = new QLineEdit;
    lnEdit->setReadOnly(true);
 
    QLabel *countryLabel = new QLabel(tr("Country:"));
    cEdit = new QLineEdit;
    cEdit->setReadOnly(true);
 
    QLabel *cityLabel = new QLabel(tr("City:"));
    cityEdit = new QLineEdit;
    cityEdit->setReadOnly(true);
 
    newButton = new QPushButton(tr("&New"));
    nextButton = new QPushButton(tr("&Next"));
    previousButton = new QPushButton(tr("&Previous"));
    saveButton = new QPushButton(tr("&Save"));
    deleteButton = new QPushButton(tr("&Delete"));
 
    connect(newButton, SIGNAL(clicked()), this, SLOT(on_newButton_clicked()));
    connect(nextButton, SIGNAL(clicked()), mapper, SLOT(toNext()));
    connect(previousButton, SIGNAL(clicked()), mapper, SLOT(toPrevious()));
    connect(saveButton, SIGNAL(clicked()), this, SLOT(on_saveButton_clicked()));
    connect(deleteButton, SIGNAL(clicked()), this, SLOT(on_deleteButton_clicked()));
 
    QGridLayout *mainLayout = new QGridLayout;
    mainLayout->addWidget(tableView);
    mainLayout->addWidget(fnLabel);
    mainLayout->addWidget(fEdit);
    mainLayout->addWidget(lnLabel);
    mainLayout->addWidget(lnEdit);
    mainLayout->addWidget(countryLabel);
    mainLayout->addWidget(cEdit);
    mainLayout->addWidget(cityLabel);
    mainLayout->addWidget(cityEdit);
    mainLayout->addWidget(newButton);
    mainLayout->addWidget(nextButton);
    mainLayout->addWidget(previousButton);
    mainLayout->addWidget(saveButton);
    mainLayout->addWidget(deleteButton);
 
    setLayout(mainLayout);
    setWindowTitle(tr("Application Layout"));
 
 
    //Model setup
    tableModel = new QSqlTableModel(this);
    tableModel->setEditStrategy(QSqlTableModel::OnFieldChange);
    tableModel->setTable("application");
    tableModel->select();
    tableModel->setHeaderData(0, Qt::Horizontal, tr("First Name"));
    tableModel->setHeaderData(1, Qt::Horizontal, tr("Last Name"));
    tableModel->setHeaderData(2, Qt::Horizontal, tr("Country"));
    tableModel->setHeaderData(3, Qt::Horizontal, tr("City"));
 
    fnLabel->setBuddy(fEdit);
    lnLabel->setBuddy(lnEdit);
    countryLabel->setBuddy(cEdit);
    cityLabel->setBuddy(cityEdit);
 
    //Mapper
    mapper = new QDataWidgetMapper(this);
    mapper->setModel(tableModel);
    mapper->addMapping(fEdit, 0);
    mapper->addMapping(lnEdit, 1);
    mapper->addMapping(cEdit, 2);
    mapper->addMapping(cityEdit, 3);
    mapper->setSubmitPolicy(QDataWidgetMapper::AutoSubmit);
    mapper->toFirst();
 
 
    //TableView
    tableView = new QTableView(this);
    tableView->setModel(tableModel);
    tableView->resizeColumnsToContents();
    tableView->setWindowTitle("Application Data");
}
 
void smith::setupModel()
{
    QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
    db.setDatabaseName("smith.DAT");
    if (!db.open()) {
        QMessageBox::critical(0, tr("Cannot open database"),
            tr("Unable to establish a database connection.\n"
               "This example needs SQLite support. Please read "
               "the Qt SQL driver documentation for information how "
               "to build it."), QMessageBox::Cancel);
        return;
    }
}
void smith::on_newButton_clicked()
{
 
}
 
 
void smith::on_saveButton_clicked()
{
 
}
 
void smith::on_deleteButton_clicked()
{
 
}

main.cpp

Code:

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

How do i get the qtableview,the buttons and the forms to display correctly?.