program a Qt demo

I assume that your environment is OK to program a Qt.By the way all code is done on Ubuntu.
Step1: program a Qt demo in QtProject folder.

#include <QApplication>
#include <QLabel>
#include <QWidget>

int main(int argc, char *argv[])
{
        QApplication app(argc,argv);
        QLabel hello("<center>Welcome to my first Qt program</center>");
        hello.setWindowTitle("My first Qt program");
        hello.resize(400,400);
        hello.show();
        return app.exec();
}

To save above code in a file testmain.cpp.
Step2: generate a ​​.pro​​​ file which is used to generate a ​​Makefile​​

~/QtProject$ qmake -project
~/QtProject$ ls
QtProject.pro  testmain.cpp

Step3: add ​​QT += gui widgets​​​ to the end of QtProject.pro file.
Step4: to generate a ​​Makefile​​ file which is used to compile the program.

~/QtProject$ qmake QtProject.pro
kyunban@kyunban:~/QtProject$ ls
Makefile  QtProject.pro  testmain.cpp

Step5: compile this program

~/QtProject$ make
~/QtProject$ ls
Makefile  QtProject  QtProject.pro  testmain.cpp  testmain.o

Finally, we get a executable file ​​QtProject​​,run it with below command:

~/QtProject$ ./QtProject