#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QStringList tauList;
    tauList << "1" << "0.1" << "0.01" << "0.001" << "0.0001";
    ui->tauComboBox->addItems(tauList);
}

MainWindow::~MainWindow()
{
    delete ui;
}

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

--- 
+++ 
@@ -6,6 +6,9 @@
     ui(new Ui::MainWindow)
 {
     ui->setupUi(this);
+    QStringList tauList;
+    tauList << "1" << "0.1" << "0.01" << "0.001" << "0.0001";
+    ui->tauComboBox->addItems(tauList);
 }
 
 MainWindow::~MainWindow()
Add initialize tauComboBox in  MainWindow class constructor.
