QwtPlot + UI problem

[petromp]

[EDIT] : hmn maybe I didn't say all of this correct (and coping just a fragments of bigger code is not a good thing) so this is simple new project with my problem...

mainwindow.h :

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QMainWindow>
 
namespace Ui {
    class MainWindow;
}
 
class MainWindow : public QMainWindow
{
    Q_OBJECT
 
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
 
private:
    Ui::MainWindow *ui;
};
 
#endif // MAINWINDOW_H

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
    class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

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mainwindow.cpp

#include <qwt_plot_curve.h>
#include <qwt_plot.h>
#include <qapplication.h>
#include <qwt_symbol.h>
#include <qwt_math.h>
#include <qcolor.h>
#include <qlayout.h>
#include <qpainter.h>
#include "mainwindow.h"
#include "ui_mainwindow.h"
 
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    double x[100];
    double y[100];
 
    for(int i=0;i<100;i++)
    {
        x[i] = i/20.0;
        y[i] = 0;
    }
    QwtPlot *myPlot = new QwtPlot(this);
    // add curves
    QwtPlotCurve *curve = new QwtPlotCurve();
    curve->setRawSamples(x, y, 100);
    curve->setSymbol(new QwtSymbol(QwtSymbol::Cross, Qt::NoBrush,
        QPen(Qt::black), QSize(5, 5) ) );
    curve->setPen(QColor(Qt::darkGreen));
    curve->setStyle(QwtPlotCurve::Lines);
    curve->setCurveAttribute(QwtPlotCurve::Fitted);
    curve->attach(myPlot);
    this->setCentralWidget(myPlot);
    myPlot->autoReplot();
    myPlot->replot();
}
 
MainWindow::~MainWindow()
{
    delete ui;
}

#include <qwt_plot_curve.h>
#include <qwt_plot.h>
#include <qapplication.h>
#include <qwt_symbol.h>
#include <qwt_math.h>
#include <qcolor.h>
#include <qlayout.h>
#include <qpainter.h>
#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    double x[100];
    double y[100];

    for(int i=0;i<100;i++)
    {
        x[i] = i/20.0;
        y[i] = 0;
    }
    QwtPlot *myPlot = new QwtPlot(this);
    // add curves
    QwtPlotCurve *curve = new QwtPlotCurve();
    curve->setRawSamples(x, y, 100);
    curve->setSymbol(new QwtSymbol(QwtSymbol::Cross, Qt::NoBrush,
        QPen(Qt::black), QSize(5, 5) ) );
    curve->setPen(QColor(Qt::darkGreen));
    curve->setStyle(QwtPlotCurve::Lines);
    curve->setCurveAttribute(QwtPlotCurve::Fitted);
    curve->attach(myPlot);
    this->setCentralWidget(myPlot);
    myPlot->autoReplot();
    myPlot->replot();
}

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

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main.cpp

#include <qwt_plot_curve.h>
#include <qwt_plot.h>
#include <QApplication>
#include <qwt_symbol.h>
#include <qwt_math.h>
#include <qcolor.h>
#include <QDebug>
#include <QPushButton>
#include <qlayout.h>
#include <qpainter.h>
#include "mainwindow.h"
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
/*
    QWidget w;
    double x[100];
    double y[100];
 
    for(int i=0;i<100;i++)
    {
        x[i] = i/20.0;
        y[i] = sin(x[i]);
    }
    QHBoxLayout *layout = new QHBoxLayout(&w);
    layout->setContentsMargins( 0, 0, 0, 0 );
    QwtPlot *myPlot = new QwtPlot(&w);
    myPlot->setMinimumSize(w.geometry().width()-20,w.geometry().height()-20);
    myPlot->updateGeometry();
    // add curves
    QwtPlotCurve *curve = new QwtPlotCurve();
    curve->setRawSamples(x, y, 100);
    curve->setSymbol(new QwtSymbol(QwtSymbol::Cross, Qt::NoBrush,
        QPen(Qt::black), QSize(5, 5) ) );
    curve->setPen(QColor(Qt::darkGreen));
    curve->setStyle(QwtPlotCurve::Lines);
    curve->setCurveAttribute(QwtPlotCurve::Fitted);
    curve->attach(myPlot);
    layout->addWidget(myPlot);
    w.update();
*/
    MainWindow w;
    w.show();
 
    return a.exec();
}

#include <qwt_plot_curve.h>
#include <qwt_plot.h>
#include <QApplication>
#include <qwt_symbol.h>
#include <qwt_math.h>
#include <qcolor.h>
#include <QDebug>
#include <QPushButton>
#include <qlayout.h>
#include <qpainter.h>
#include "mainwindow.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
/*
    QWidget w;
    double x[100];
    double y[100];

    for(int i=0;i<100;i++)
    {
        x[i] = i/20.0;
        y[i] = sin(x[i]);
    }
    QHBoxLayout *layout = new QHBoxLayout(&w);
    layout->setContentsMargins( 0, 0, 0, 0 );
    QwtPlot *myPlot = new QwtPlot(&w);
    myPlot->setMinimumSize(w.geometry().width()-20,w.geometry().height()-20);
    myPlot->updateGeometry();
    // add curves
    QwtPlotCurve *curve = new QwtPlotCurve();
    curve->setRawSamples(x, y, 100);
    curve->setSymbol(new QwtSymbol(QwtSymbol::Cross, Qt::NoBrush,
        QPen(Qt::black), QSize(5, 5) ) );
    curve->setPen(QColor(Qt::darkGreen));
    curve->setStyle(QwtPlotCurve::Lines);
    curve->setCurveAttribute(QwtPlotCurve::Fitted);
    curve->attach(myPlot);
    layout->addWidget(myPlot);
    w.update();
*/
    MainWindow w;
    w.show();

    return a.exec();
}

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mainwindow.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>400</width>
    <height>300</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <widget class="QWidget" name="centralWidget"/>
 </widget>
 <layoutdefault spacing="6" margin="11"/>
 <resources/>
 <connections/>
</ui>

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>400</width>
    <height>300</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <widget class="QWidget" name="centralWidget"/>
 </widget>
 <layoutdefault spacing="6" margin="11"/>
 <resources/>
 <connections/>
</ui>

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two outcomes (on screens you can see which part of main function was commented which not)



and second



the question is : why first outcome is like that ? it paints only first point where is the rest ?