QT: modal, modeless, text box, button, single line input box

One 、 Modal, non modal

#include "widget.h"

#include <QApplication>
#include <QDialog>
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget w;
QDialog dia(&w);                                                    
                                                                    
QLabel lab("Hello",&w);                                             
lab.setGeometry(100,300,200,100);                                   
 QObject::connect(&but,&QPushButton::clicked,&lab,&QLabel::clear);  
lab.setStyleSheet("font:25px;color:blue");                          
lab.setText("<a href = www.baidu.com> use Baidu Search ");                        
lab.setToolTip(" Show me URL");                                          
lab.setToolTipDuration(1000);                                       
                                                                    
QObject::connect(&lab,&QLabel::linkActivated,&lab,&QLabel::clear);
QObject::connect(&lab,&QLabel::linkActivated,&lab,&QLabel::setText);
dia.setModal(true);                                               
dia.show();                                                       
                                                                    
                                                                    
dia.exec(); 
     w.show();
    return a.exec();
}                                                      

Two 、 The text box

#include "widget.h"

#include <QApplication>
#include <QDialog>
#include <QLabel>
#include <QPushButton>
#include <QLineEdit>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget w;
 QLabel lab(&w);                                                     
 lab.setText("Hello Qt");                                            
 lab.setGeometry(50,100,150,100);                                    
 lab.setStyleSheet("font:20px;color:blue");                          
 lab.move(300,200);                                                  
                                                                    
 lab.setText("<a href = \"www.baidu.com\"> Baidu ");                      
 lab.setToolTip(" Click to display URL");                                          
 lab.setToolTipDuration(1000);                                       
                                                                     
 QObject::connect(&lab,&QLabel::linkActivated,&lab,&QLabel::setText);
     w.show();
    return a.exec();
}

3、 ... and 、 Button

#include "widget.h"

#include <QApplication>
#include <QDialog>
#include <QLabel>
#include <QPushButton>
#include <QLineEdit>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget w;
 QPushButton but1(" close ",&dia);
    but1.move(10,10);
   but1.show();


    but1.setAutoDefault(false);
    QObject::connect(&but1,&QPushButton::clicked,&dia,&QDialog::close);
     w.show();
    return a.exec();
}

Four 、 Single line input box

#include "widget.h"

#include <QApplication>
#include <QDialog>
#include <QLabel>
#include <QPushButton>
#include <QLineEdit>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget w;
QLineEdit ed(&w);
    ed.move(100,200);
    ed.setPlaceholderText(" Please enter ...");
    ed.setClearButtonEnabled(true);

    ed.setEchoMode(QLineEdit::Password);

    QLabel lab(&w);
    lab.move(100,100);
    QObject::connect(&ed,&QLineEdit::textChanged,&lab,&QLabel::setText);
   w.show();
    return a.exec();
}