列表插入

向有序列表插入一新元素。不是很友好的做法：

list l = (list) malloc(sizeof(struct list));
l -> val = val;
if(the_list == NULL || the_list -> val >= val)
  {
    /* insert the element first */
    l -> next = the_list;
    the_list = l;
  } else {
  list q = the_list;
  list p = q -> next;
  for(; p && p -> val < val; q = p, p = p -> next)
    ;
  l -> next = p;
  q -> next = l;
 }

更加 idiom 的做法：

list *p;
list l = (list) malloc(sizeof(struct list));
l -> val = val;
for(p = &the_list; *p && (*p) -> val < val; p = &((*p) -> next))
  ;
l -> next = *p;
*p = l;