7. 例子

   /*
     * Determine if the sky is blue by checking that it isn't night.
     * CAVEAT: Only sometimes right.  May return TRUE when the answer
     * is FALSE.  Consider clouds, eclipses, short days.
     * NOTE: Uses 'hour' from 'hightime.c'.  Returns 'int' for
     * compatibility with the old version.
     */
    int                             /* true or false */
    skyblue()
    {
            extern int      hour;           /* current hour of the day */
    
            return (hour >= MORNING && hour <= EVENING);
    }

    /*
     * Find the last element in the linked list
     * pointed to by nodep and return a pointer to it.
     * Return NULL if there is no last element.
     */
    node_t *
    tail(nodep)
            node_t  *nodep;                 /* pointer to head of list */
    {
            register node_t *np;            /* advances to NULL */
            register node_t *lp;            /* follows one behind np */
    
            if (nodep == NULL)
                    return (NULL);
            for (np = lp = nodep; np != NULL; lp = np, np = np->next)
                    ;       /* VOID */
            return (lp);
    }