Chapter-4/4-4/polishcalc.c
/* duplicate:  duplicates the top element of the stack */
duplicates the top element of the stack
duplicates the top element of the stack
void duplicate_top(void) {
  double tmp = pop();
  push(tmp);
  push(tmp);
}
void duplicate_top ( void ) { double tmp = pop ( ) ; push ( tmp ) ; push ( tmp ) ; }
duplicate:  duplicates the top element of the stack
duplicate : duplicates the top element of the stack