Stack Handling in C

• Initialize a stack s to Empty:

  
     s = NULL;
  

• Test if stack s is not Empty:

  
     if ( s != NULL ) ... 
  

• Push an item newtok onto stack s:

  
     newtok->link = s;
     s = newtok;
  

  or:

  
     s = cons(newtok,s);
  

• Pop stack s to yield item top:

  
     top = s;
     s = s->link;   /* s = rest(s) */