#include <iostream>
using namespace std;

int main() {
 cout << "Hello World!";
 return 0;
} 

CXX = g++ # ___________________________________________ Define the C++ compiler to use (g++)
SRC = hello_world.cpp # _______________________________ Define the main source
TARGET = hello_world # ________________________________ Define the name of the output executable

all: $(TARGET) # ______________________________________ The 'all' target is the default when you run 'make'

$(TARGET): $(SRC) # ___________________________________ Rule to build the executable from source file
   @echo "Starting build..."
   $(CXX) $(SRC) -o $(TARGET)
   @echo "Run with ./"$(TARGET)
   @echo "to force rebuild use: make -B"

clean: # ______________________________________________ A common target to clean up generated files
   rm -f $(TARGET) *.o

g++ hello_world.cpp -o hello

Hello World!

click here for old / failed LOG

but to code a desktop app // opening a window in desktop and use keyboard and mouse in it
is much more difficult than that 'hello_world' terminal app

QT

try QT 5 first:
sudo apt install qttools5-dev-tools
sudo apt install qtcreator
( where QT Creator itself is QT6 already )
Go to menu help > about plugins
Uncheck device support > remote linux


Restart Qt Creator

possibly needed??

sudo apt install qtdeclarative5-dev
sudo apt install xterm
sudo apt install git-core
sudo apt install subversion

Creating your first project in Qt Creator is
a straightforward process guided by wizards. You can choose between different application types, such as Qt Widgets (for traditional desktop UIs) or Qt Quick (for dynamic, modern UIs using QML), and languages like C++ or Python.
Steps to Create a New Qt Project

Open Qt Creator and go to the Welcome page.
Select Projects from the left pane, and then click New Project. This will open the New Project dialog.
Choose a project template. For a general-purpose C++ desktop application, select Application (Qt) > Qt Widgets Application > Choose.
Name your project and choose a location on your computer to store the project files. It's recommended to keep all projects in a central workspace. Then, click Next or Continue.
Configure project details (this step may vary depending on the template chosen). For a Qt Widgets application, you might define class information (e.g., MainWindow as class name, QMainWindow as base class).
Select the build system. You can typically choose between CMake, qmake, or Qbs. If you are new to Qt, the default option (often CMake) is usually fine.
Select the kits you want to use. A "kit" defines the build environment, including the compiler, Qt version, and device type (e.g., desktop, Android, etc.). Most likely, you will only have one desktop kit available, which you should select.
Review the project settings and click Finish (or Done on macOS) to create the project files.

Build and Run Your Project
Once the project is created, Qt Creator will generate the necessary initial files (like a main file, project file, and UI file).

To run your application, simply press the green Run button (usually a green play icon) in the bottom-left corner of the interface or go to Build > Run in the menu.
The application will compile and then launch, displaying an empty window based on the template you selected.

For detailed tutorials and official documentation, you can visit the Qt Documentation website.

first make a new project directory
mkdir ~/Projects/CPP/Qt_start
cd ~/Projects/CPP/Qt_start

start Qt creator

[ Create Project ] [Application (Qt) ] [ Qt Widgets Application ] [Choose]
name: QT_start
path: ~/Projects/CPP/Qt_start
[next]
CMake[next][next]
Kits ?problem?

[Edit][Preferences][Kit][Add] ( or better select 'Desktop' and [duplicate] rename to
Name: Qt_settings
[Apply]
still Kits ?problem?

---

missing qmake:
sudo apt install qt5-qmake
qmake --version

QMake version 3.1
Using Qt version 5.15.15 in /usr/lib/aarch64-linux-gnu

ok but not for:
sudo apt install qt6-qmake
Error: Unable to locate package qt6-qmake

but
sudo apt install qt6ct

qt6ct is already the newest version (0.10-2+b1).

( possibly by the QT creator installation )

found:
sudo apt install qt6-base-dev libvulkan-dev qmake6 qmake6-bin qt6-qpa-plugins

---

anyhow: still problems in Kit,
now missing cmake:
sudo apt install cmake cmake-doc cmake-format elpa-cmake-mode
kit: CMake Tool:
System CMake at /usr/bin/cmake (Default)
Generator Ninja


still / again problems in Kit:
QT version: QT 5.15.15 (qt5)
Error: QT version not properly installed

---

try back to use VS Code:
code .

from [Extensions] install
Qt Extension Pack
Qt C++

---

/qtsize/build $ cmake ..
bash: cmake: command not found

08:28:27: Starting: "/usr/bin/cmake" --build /home/pi/Projects/CPP/qtsize/build --target clean
08:28:28: The process "/usr/bin/cmake" exited normally.
08:28:28: Starting: "/usr/bin/cmake" --build /home/pi/Projects/CPP/qtsize/build --target all
[ 0%] Built target qtsize_autogen_timestamp_deps
[ 16%] Automatic MOC and UIC for target qtsize
[ 16%] Built target qtsize_autogen
[ 33%] Building CXX object CMakeFiles/qtsize.dir/qtsize_autogen/mocs_compilation.cpp.o
[ 50%] Building CXX object CMakeFiles/qtsize.dir/src/MainWindow.cxx.o
[ 66%] Building CXX object CMakeFiles/qtsize.dir/src/main.cxx.o
[ 83%] Linking CXX executable qtsize
[100%] Built target qtsize
08:28:50: The process "/usr/bin/cmake" exited normally.
08:28:50: Elapsed time: 00:23.

g++ hello_world.cpp -o hello_world

[Desktop Entry]
Name=qtstart
Comment=Run My first C++ Qt Desktop Application
Exec=/home/pi/Projects/CPP/teststart/qtstart
Icon=/path/to/icon.png
Terminal=false
Type=Application
Categories=Utility;

Python 3.13.5

import sys
import random
from PySide6 import QtCore, QtWidgets, QtGui

class MyWidget(QtWidgets.QWidget):
 def __init__(self):
 super().__init__()

 self.hello = ["Hallo Welt", "Hei maailma", "Hola Mundo", "?????? ???"]

 self.button = QtWidgets.QPushButton("Click me!")
 self.text = QtWidgets.QLabel("Hello World",
 alignment=QtCore.Qt.AlignCenter)

 self.layout = QtWidgets.QVBoxLayout(self)
 self.layout.addWidget(self.text)
 self.layout.addWidget(self.button)

 self.button.clicked.connect(self.magic)

 @QtCore.Slot()
 def magic(self):
 self.text.setText(random.choice(self.hello))



if __name__ == "__main__":
 app = QtWidgets.QApplication([])

 widget = MyWidget()
 widget.resize(800, 600)
 widget.show()

 sys.exit(app.exec())

-1- QT Creator as IDE

-2- Qt Designer

 self.ui.le_key.returnPressed.connect(self.on_key_Input)

 def on_key_Input(self):
 print ( f"key {self.ui.le_key.text()}" )