main.c

#include <gtk/gtk.h>

static void on_activate (GtkApplication *app) {
    // Create a new window
    GtkWidget *window = gtk_application_window_new (app);
    // Create a new button
    GtkWidget *button = gtk_button_new_with_label ("Hello, World!");
    // When the button is clicked, close the window passed as an argument
    g_signal_connect_swapped (button, "clicked", G_CALLBACK (gtk_window_close), window);
    gtk_window_set_child (GTK_WINDOW (window), button);
    gtk_window_present (GTK_WINDOW (window));
}

int main(int argc, char **argv) {
    // Create a new application
    GtkApplication *app = gtk_application_new ("com.example.GtkApplication",
                                               G_APPLICATION_FLAGS_NONE);
    g_signal_connect (app, "activate", G_CALLBACK (on_activate), NULL);
    return g_application_run (G_APPLICATION (app), argc, argv);
}