DouKaku?

#include <stdio.h>
#include <X11/Xlib.h>

int main(int argc, char *argv[])
{
    Display *display;
    Window  window;
    char    *title = "こんにちは、GUI！";
    int     x_size = 400;
    int     y_size = 300;

    display = XOpenDisplay(NULL);
    window = XCreateSimpleWindow(display, DefaultRootWindow(display),
                                 DisplayWidth(display, 0)/2,
                                 DisplayHeight(display, 0)/2,
                                 x_size, y_size, 50,
                                 BlackPixel(display, 0),
                                 WhitePixel(display, 0));
    XSetStandardProperties(display, window, title, NULL,
                           None, argv, argc, NULL);
    XMapWindow(display, window);
    XFlush(display);

    getchar();
    XCloseDisplay(display);

    return 0;
}