now working...
form1.cpp
Qt Code: 
  1. #include "form1.h"
  2. #include "ui_form1.h"
  3.  
  4. #include <QTimer>
  5. #include <QTime>
  6.  
  7.  
  8. Form1::Form1(QWidget *parent) :
  9.     QWidget(parent),
  10.     ui(new Ui::Form1)
  11. {
  12.     ui->setupUi(this);
  13.  
  14.  
  15.    time.setHMS(0,0,0,0);
  16.    i=0;
  17.    ui->lcdNumber->setNumDigits(8);
  18.    QString text = time.toString("hh:mm:ss");
  19.    ui->lcdNumber->display(text);
  20. }
  21.  
  22. Form1::~Form1()
  23. {
  24.     delete ui;
  25. }
  26.  
  27. void Form1::startTime()
  28. {
  29.     timer=new QTimer(this);
  30.     connect(timer, SIGNAL(timeout()), this, SLOT(showTime()));
  31.     timer->start(1000);
  32. }
  33.  
  34. void Form1::showTime()
  35. {
  36.     QTime newtime;
  37.     i=i+1;
  38.     newtime=time.addSecs(i);
  39.     QString text = newtime.toString("hh:mm:ss");
  40.     ui->lcdNumber->display(text);
  41.  
  42. }
  43.  
  44. void Form1::stopTime()
  45. {
  46.     timer->stop();
  47. }
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form1.h
Qt Code: 
  1. #ifndef FORM1_H
  2. #define FORM1_H
  3.  
  4. #include <QString>           
  5.  
  6. #include <QWidget>
  7.  
  8. #include <QTimer>
  9. #include <QTime>
  10.  
  11.  
  12. namespace Ui {
  13.     class Form1;
  14. }
  15.  
  16. class Form1 : public QWidget
  17. {
  18.     Q_OBJECT
  19.  
  20. public:
  21.     explicit Form1(QWidget *parent = 0);
  22.     ~Form1();
  23.     int i;
  24.  
  25. private:
  26.     Ui::Form1 *ui;
  27.  
  28.  
  29. private:               
  30.     QTime time;
  31.  
  32. public:
  33.     QTimer *timer;
  34.  
  35. public slots:
  36.     void startTime();
  37.     void showTime();
  38.     void stopTime();
  39.  
  40. };
  41. #endif // FORM1_H
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