how i can increase the size of my plots and have a good organisation of this widget ?

[Santosh Reddy]

Ok, I took a small liberty to modify your code hope you don't mine it. This would make all the plots expand to the window size, and also not allow the window to be smaller than a certain size. I checked its working on my machine.
QwtLayout.jpg
main.cpp

#include <QApplication>
#include "MyMainWindow.h"
#include <QGridLayout>
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    MyMainWindow fenetre;
    fenetre.show();
    return app.exec();
}

#include <QApplication>
#include "MyMainWindow.h"
#include <QGridLayout>
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    MyMainWindow fenetre;
    fenetre.show();
    return app.exec();
}

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MyMainWindow.h

#ifndef MYMAINWINDOW_H
#define MYMAINWINDOW_H
 
#include <QApplication>
#include <QWidget>
#include <QPushButton>
#include <QMessageBox>
#include <qwt_plot.h>
 
class MyMainWindow : public QWidget
{
    Q_OBJECT
 
public:
    explicit MyMainWindow(QWidget* parent = 0);
 
private:
    QPushButton *BUTTONRun;
    QPushButton *BUTTONQuit;
    QPushButton *BUTTONAbout;
    QPushButton *BUTTONContact;
 
    QwtPlot *myPlot1;
    QwtPlot *myPlot2;
    QwtPlot *myPlot3;
    QwtPlot *myPlot4;
    QwtPlot *myPlot5;
    QwtPlot *myPlot6;
};
#endif // MYMAINWINDOW_H

#ifndef MYMAINWINDOW_H
#define MYMAINWINDOW_H

#include <QApplication>
#include <QWidget>
#include <QPushButton>
#include <QMessageBox>
#include <qwt_plot.h>

class MyMainWindow : public QWidget
{
    Q_OBJECT

public:
    explicit MyMainWindow(QWidget* parent = 0);

private:
    QPushButton *BUTTONRun;
    QPushButton *BUTTONQuit;
    QPushButton *BUTTONAbout;
    QPushButton *BUTTONContact;

    QwtPlot *myPlot1;
    QwtPlot *myPlot2;
    QwtPlot *myPlot3;
    QwtPlot *myPlot4;
    QwtPlot *myPlot5;
    QwtPlot *myPlot6;
};
#endif // MYMAINWINDOW_H

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MyMainWindow.cpp

#include "MyMainWindow.h"
#include <QGridLayout>
#include <QHBoxLayout>
 
MyMainWindow::MyMainWindow(QWidget* parent) : QWidget(parent)
{
    QGridLayout* mainLayout = new QGridLayout();
    setLayout(mainLayout);
 
    myPlot1 = new QwtPlot();
    myPlot2 = new QwtPlot();
    myPlot3 = new QwtPlot();
    myPlot4 = new QwtPlot();
    myPlot5 = new QwtPlot();
    myPlot6 = new QwtPlot();
 
    myPlot1->setMinimumSize(200, 100);
    myPlot2->setMinimumSize(200, 100);
    myPlot3->setMinimumSize(200, 100);
    myPlot4->setMinimumSize(200, 100);
    myPlot5->setMinimumSize(200, 100);
    myPlot6->setMinimumSize(200, 100);
 
    QWidget* buttonWidget = new QWidget();
    QGridLayout* buttonLayout = new QGridLayout();
 
    BUTTONRun = new QPushButton("RUN");
    BUTTONQuit = new QPushButton("STOP");
    BUTTONAbout = new QPushButton("About");
    BUTTONContact = new QPushButton("Contact");
 
    buttonLayout->addWidget(BUTTONRun    ,0,0);
    buttonLayout->addWidget(BUTTONQuit   ,0,1);
    buttonLayout->addWidget(BUTTONAbout  ,1,0);
    buttonLayout->addWidget(BUTTONContact,1,1);
 
    buttonWidget->setLayout(buttonLayout);
 
    mainLayout->addWidget(myPlot1      ,0,0,1,1);
    mainLayout->addWidget(myPlot2      ,0,1,1,1);
    mainLayout->addWidget(myPlot3      ,0,2,1,1);
    mainLayout->addWidget(myPlot4      ,1,0,1,1);
    mainLayout->addWidget(myPlot5      ,1,1,1,1);
    mainLayout->addWidget(myPlot6      ,1,2,1,1);
    mainLayout->addWidget(buttonWidget ,0,3,1,1);
 
    QObject::connect(BUTTONQuit, SIGNAL(clicked()), qApp, SLOT(quit()));
    QObject::connect(BUTTONAbout, SIGNAL(clicked()), qApp, SLOT(aboutQt()));
}

#include "MyMainWindow.h"
#include <QGridLayout>
#include <QHBoxLayout>

MyMainWindow::MyMainWindow(QWidget* parent) : QWidget(parent)
{
    QGridLayout* mainLayout = new QGridLayout();
    setLayout(mainLayout);

    myPlot1 = new QwtPlot();
    myPlot2 = new QwtPlot();
    myPlot3 = new QwtPlot();
    myPlot4 = new QwtPlot();
    myPlot5 = new QwtPlot();
    myPlot6 = new QwtPlot();

    myPlot1->setMinimumSize(200, 100);
    myPlot2->setMinimumSize(200, 100);
    myPlot3->setMinimumSize(200, 100);
    myPlot4->setMinimumSize(200, 100);
    myPlot5->setMinimumSize(200, 100);
    myPlot6->setMinimumSize(200, 100);

    QWidget* buttonWidget = new QWidget();
    QGridLayout* buttonLayout = new QGridLayout();

    BUTTONRun = new QPushButton("RUN");
    BUTTONQuit = new QPushButton("STOP");
    BUTTONAbout = new QPushButton("About");
    BUTTONContact = new QPushButton("Contact");

    buttonLayout->addWidget(BUTTONRun    ,0,0);
    buttonLayout->addWidget(BUTTONQuit   ,0,1);
    buttonLayout->addWidget(BUTTONAbout  ,1,0);
    buttonLayout->addWidget(BUTTONContact,1,1);

    buttonWidget->setLayout(buttonLayout);

    mainLayout->addWidget(myPlot1      ,0,0,1,1);
    mainLayout->addWidget(myPlot2      ,0,1,1,1);
    mainLayout->addWidget(myPlot3      ,0,2,1,1);
    mainLayout->addWidget(myPlot4      ,1,0,1,1);
    mainLayout->addWidget(myPlot5      ,1,1,1,1);
    mainLayout->addWidget(myPlot6      ,1,2,1,1);
    mainLayout->addWidget(buttonWidget ,0,3,1,1);

    QObject::connect(BUTTONQuit, SIGNAL(clicked()), qApp, SLOT(quit()));
    QObject::connect(BUTTONAbout, SIGNAL(clicked()), qApp, SLOT(aboutQt()));
}

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