I'm glad to see that setjmp() and longjmp() are still allowed. I'm just kidding by the way. For those C programmers who haven't encountered these before, it is a powerful way to do a "goto" in C. Powerful in the sense that you can jump anywhere, not limited to the same function. If it's used at all these days, it's used for exception handling. More info: https://en.wikipedia.org/wiki/Setjmp.h
I had quite some fun playing around with it to obfuscate code. I did find that jumping to a different position in the same expression broke on a lot of compilers as soon as optimization was turned on.
Here's a simple program to output a string with the characters in an unusual order.
#include
#include
#define J(x,y) (longjmp(x,y),0)
int main(int argc, char **argv)
{
jmp_buf j[011];
int x,X=0;
signed char* i = " eehcef lo u ef'oYurls " +021;
(x=setjmp(j[X++]))?J(j[x],*++i):((x=setjmp(j[X++]))?J(x[j],*--i):((x=
setjmp(j[X++]))?J(x[j],(putchar(*i),*i+=128)):(x=setjmp(j[++X]))?((x>X)?J(1[j],6):J(1[j],3
)):(x=setjmp(j[++X]))?((x&0x80)?J(1[j],7):J(1[j],5)):(x=setjmp(j[++X]
))?(((X=0)?J(j[2],6):0));
return 0;
}