Valculator/main.vala

public class Main : Gtk.Application {
	public Main() {
		Object (application_id: "com.example.App");
	}

	public override void activate () {
		var win = new Gtk.ApplicationWindow (this);
		win.set_title("Calculator");

		var display = new Gtk.Label("Display");
		display.xalign = 1.0f;
		var grid = new Gtk.Grid();

		grid.attach(display, 0, 0, 3);
		// Procedurlly generating numbered buttons 1-9
		for (int col = 0; col < 3; col++) {
			for (int row = 0; row < 3; row++){
				// This math is need to orient the buttons in the correct order
				// starting from bottom left to top right
				var number = (3 - row - 1)*3 + col + 1;
				var btn = new Gtk.Button.with_label("%d".printf(number));
				grid.attach(btn, col, row+1);
			}
		}

		var zero = new Gtk.Button.with_label("0");
		var equal = new Gtk.Button.with_label("=");
		grid.attach(zero, 0, 4);
		grid.attach(equal, 1, 4);

		win.child = grid;
		win.present ();
	}

	public static int main (string[] args) {
		var app = new Main();
		return app.run (args);
	}
}