Found a qute hello world program, the code is:
#define _________ }
#define ________ putchar
#define _______ main
#define _(a) ________(a);
#define ______ _______(){
#define __ ______ _(0x48)_(0x65)_(0x6C)_(0x6C)
#define ___ _(0x6F)_(0x20)_(0x77)_(0x6F)_(0x72)
#define ____ _(0x6C)_(0x64)_(0x21)_(0x0A)
#define _____ __ ___ ____ _________
#include <stdio.h>
_____
Though it is hard to read, it's not so hard to understand. And it is kind of fun. 🙂