add the content of Quack

Author: UbuntuLover

linkedlist/README.md

@@ -38,6 +38,202 @@ public class Linkedlist {
 
 如果想要删除单链表上的节点， 也非常简单，就是删除过程的逆过程。这里不再赘述。
 
+###　拓展
+网上链表相关的代码有比较多，这里可以考虑使用链表来实现队列/栈。
+队列：一种先进先出的结构
+栈：　一种先进后出的结构
+
+可以看到，栈和队列非常相似。
+好了，还是程序猿那句老话，**talk is cheap, show me the code.**
+我们来设计一个接口，又可以当栈用，也可以当队列用。栈叫Stack， 队列叫Queue， 那么我们称之为Quack。
+
+---
+Quack.h的内容：
+```c
+#include<stdio.h>
+#include <stdlib.h>
+
+typedef struct _node* Quack;
+
+
+Quack createQuack(void);    // create and return Quack
+Quack destroyQuack(Quack);  // remove the Quack 
+void  push(int, Quack);     // put the given integer onto the top of the quack
+void  qush(int, Quack);     // put the given integer onto the bottom of the quack
+int   pop(Quack);           // pop and return the top element on the quack
+int   isEmptyQuack(Quack);  // return 1 is Quack is empty, else 0
+void  makeEmptyQuack(Quack);// remove all the elements on Quack
+void  showQuack(Quack);     // print the contents of Quack, from the top down
+
+```
+
+在头文件里面写好了函数定义，我们来考虑实现功能。
+
+Quack.c
+```c
+#include "Quack.h"
+#include <limits.h> // for INT_MAX macro.
+
+#define MARKERDATA INT_MAX // dummy data
+
+struct node {
+   int data;
+   struct node *next;
+};
+
+Quack createQuack(void) {
+   Quack marker;
+   marker = malloc(sizeof(struct node));
+   if (marker == NULL) {
+      fprintf (stderr, "createQuack: no memory, aborting\n");
+      exit(1);
+   }
+   marker->data = MARKERDATA; // should never be used
+   marker->next = NULL;
+   return marker;
+}
+
+void push(int data, Quack qs) {
+   Quack newnode;
+   if (qs == NULL) {
+      fprintf(stderr, "push: quack not initialised\n");
+   }
+   else {
+      newnode = malloc(sizeof(struct node));
+      if (newnode == NULL) {
+         fprintf(stderr, "push: no memory, aborting\n");
+         exit(1);
+      }
+      newnode->data = data;
+      newnode->next = qs->next;
+      qs->next = newnode;
+   }
+   return;
+}
+
+void qush(int data, Quack qs) {
+
+   // code not shown
+
+   return;
+}
+
+int pop(Quack qs) {
+   int retval = 0;
+   if (qs == NULL) {
+      fprintf(stderr, "pop: quack not initialised\n");
+   }
+   else {
+      if (isEmptyQuack(qs)) {
+         fprintf(stderr, "pop: quack underflow\n");
+      }
+      else {
+         Quack topnode = qs->next; // top dummy node is always there
+         retval = topnode->data;
+         qs->next = topnode->next;
+         free(topnode);
+      }
+   }
+   return retval;
+}
+
+Quack destroyQuack(Quack qs) { // remove the Quack  and returns NULL
+   if (qs == NULL) {
+      fprintf(stderr, "destroyQuack: quack not initialised\n");
+   }
+   else {
+      Quack ptr = qs->next;
+      while (ptr != NULL) {
+         Quack tmp = ptr->next;
+         free(ptr);
+         ptr = tmp;
+      }
+      free(qs);
+   }
+   return NULL;
+}
+
+void makeEmptyQuack(Quack qs) {
+   if (qs == NULL)
+      fprintf(stderr, "makeEmptyQuack: quack not initialised\n");
+   else {
+      while (!isEmptyQuack(qs)) {
+         pop(qs);
+      }
+   }
+   return;
+}
+
+int isEmptyQuack(Quack qs) {
+   int empty = 0;
+   if (qs == NULL) {
+      fprintf(stderr, "isEmptyQuack: quack not initialised\n");
+   }
+   else {
+      empty = qs->next == NULL;
+   }
+   return empty;
+}
+
+void showQuack(Quack qs) {
+   if (qs == NULL) {
+      fprintf(stderr, "showQuack: quack not initialised\n");
+   }
+   else {
+      printf("Quack: ");
+      if (qs->next == NULL) {
+         printf("<< >>\n");
+      }
+      else {
+         printf("<<");                 // start with <<
+         qs = qs->next;                // step over the marker link
+         while (qs->next != NULL) {
+            printf("%d, ", qs->data);  // print each element
+            qs = qs->next;
+         }
+         printf("%d>>\n", qs->data);    // last element ends with >>
+      }
+   }
+   return;
+}
+```
+
+那么我们来编写程序来使用，我们来反转字符串。
+revarg.c
+
+```c
+#include <stdio.h>
+#include <stdlib.h>
+#include "quack.h"
+
+int main(int argc, char *argv[]) {
+  Quack s = NULL;
+
+  if (argc >= 2) {
+     char *inputc = argv[1];
+     s = createQuack();
+     while (*inputc != '\0') {
+        push(*inputc++, s);
+     }
+     while (!isEmptyQuack(s)) {
+        printf("%c", pop(s));
+     }
+     putchar('\n');
+  }
+  return EXIT_SUCCESS;
+}
+```
+编译代码：
+```
+gcc Quack.c revarg.c 
+```
+运行：
+```
+./a.out 0123456789
+>> 9876543210
+```
+
+
 [LeetCode876 链表中间节点题解](linkedlist/Leetcode876MiddleOftheLinkedList.md)
 
 [Leetcode19 删除倒数n个节点题解](linkedlist/leetcode19.md)

myself/c_style_guide.md

@@ -237,5 +237,4 @@ int sum(int a, int b) {
 - 避免使用 `do {} while(condition)`, 使用while循环来替代
 - 不要使用联合体。（union）
 - 避免指针的算数操作
-- 避免类型转换。
-
+- 避免类型转换。