C absolutely guarantees that the second will NEVER be evaluated before
the first. Otherwise, things like this:

if ( ptr && ptr->field )

could fail if ptr was NULL.

In your example yes. But is there a problem if the two conditions are
independent ? for eg..

foo() {
....
  a = 0;
  b = my_complex_function_call();
  if (b && a) {
      /* Do some non-trivial stuff */
  } else {
     printf("I'm an intelligent compiler\n");
  }
.....
}

Does C guarantee that even in this case it won't be reordered and not
optimized ?

-- 
Thanks -
Manish