very first gtk program that checks that the library is installed

learning_gtk.c

#include <gtk/gtk.h>

/* to compile in ubuntu:
 *
 * sudo apt install libgtk2.0-dev
 *
 * in bash: gcc `pkg-config --cflags --libs gtk+-2.0` learning_gtk.c -o learning_gtk
 * in fish shell: gcc learning_gtk.c (pkg_config --cflags --libs gtk+-2.0 | perl -pe
 * 's/\s+/\n/g) -o learning_gtk
 */
int main(int argc, char *argv[]) {
    gtk_init(&argc, &argv);

    GtkWidget *win = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_widget_show(win);
    gtk_main();

    return 0;
}