Package gtk+-2.0 was not found in the pkg-config search path.
Perhaps you should add the directory containing `gtk+-2.0.pc'
to the PKG_CONFIG_PATH environment variable
No package 'gtk+-2.0' found
gtk1.c:1:21: error: gtk/gtk.h: No such file or directory
gtk1.c: In function 'main':
gtk1.c:5: error: 'GtkWidget' undeclared (first use in this function)
gtk1.c:5: error: (Each undeclared identifier is reported only once
gtk1.c:5: error: for each function it appears in.)
gtk1.c:5: error: 'window' undeclared (first use in this function)
gtk1.c:9: error: 'GTK_WINDOW_TOPLEVEL' undeclared (first use in this function)

=======================================================
The code I used was:

#include <gtk/gtk.h>

int main(int argc, char *argv[])
{
  GtkWidget *window;

  gtk_init (&argc, &argv);

  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  gtk_widget_show (window);

  gtk_main();
  return 0;
}
========================================================

Tried compiling with:  gcc gtk1.c -o gtk1 `pkg-config --cflags --libs gtk+-2.0`