union MyUnion u;
printf("%d\n",sizeof(union MyUnion)); prints out 8 
u.value = 999999;
printf("%llu\n",u.value); prints out 999999 
strcpy(u.s,"hello");
printf("%s\n",u.s);       prints out hello 
printf("%llu\n",u.value); Does NOT print out 999999 
                          as it has been (partly) overwritten