// vala language: valac --pkg gtk+-3.0 sample.vala

public string helloWorld(bool runTest) {

    string myString1 = "Hello";
    string myString2 = "World";

    int myNumber = 1;

    bool myTest = !! runTest; // cast to the same type (bool)

    string myOutput = "Test was disabled ...";
    if(myTest == true) {
        myOutput = myString1 + " " + myString2 + ", this is number: " + myNumber.to_string();
    }

    return myOutput;

}

public class MyApplication : Gtk.Application {

    protected override void activate() {

        string testResult = helloWorld(true);

        stdout.printf(testResult + "\n"); // print to console

        var window = new Gtk.ApplicationWindow(this); // create new window
        window.set_title("Vala Sample"); // add window title
        window.set_default_size(500, 200); // set default window size(width and height)
        var label = new Gtk.Label(testResult); // create a label
        window.add(label); // add a label to the window
        window.show_all(); // display the window

    }

}

public int main(string[] args) {

    return new MyApplication().run(args);

}

// end vala language