/* linkStack.c */

/* 链栈 */

#include <stdio.h>

#include <stdlib.h>

#include <stdbool.h>

/* 链栈数据结构 */

/*

    ————————————————

    | value | next |   <--- top

    ————————————————

                ↓

    ————————————————

    | value | next |

    ————————————————

                ↓

    ————————————————

    | value | next |

    ————————————————

*/

typedef struct node {

    int data;

    struct node *next;

} StackNode;

void interface(void);

/* 链栈函数声明 */

StackNode *initializeLinkStack();

bool isEmptyLinkStack(StackNode*);

StackNode *pushLinkStack(StackNode*, int);

StackNode *popLinkStack(StackNode*);

/* 程序主函数入口 */

int main(){

    StackNode *top = initializeLinkStack();

    int flag, num;

    interface();

    for(;;){

        printf("Command: ");

        scanf("%d", &num);

        switch(num){

            case : puts("Bye!"); return ; break;

            case :

                printf("Enter number: ");

                scanf("%d", &num);

                top = pushLinkStack(top, num);

                break;

            case :

                if(isEmptyLinkStack(top))

                    printf("Link stack is empty!\n");

                else

                    top = popLinkStack(top);

                break;

        }

    }

    return ;

}

/* 用户界面 */

void interface(void){

    puts("+******************************+");

    puts("+  0, quit      退出           +");

    puts("+  1, push      压入           +");

    puts("+  2, pop       弹出           +");

    puts("+******************************+");

}

/* 链栈函数实现 */

/* 初始化链栈 */

StackNode *initializeLinkStack(){

    StackNode *top = (StackNode*)malloc(sizeof(StackNode));

    top = NULL;

    return top;

}

/* 链栈是否为空 */

bool isEmptyLinkStack(StackNode* top){

    if(top==NULL)

        return true;

    else

        return false;

}

/* 入栈 */

StackNode *pushLinkStack(StackNode *top, int number){

    StackNode *s = (StackNode*)malloc(sizeof(StackNode));

    s->data = number;

    s->next = top;

    top = s;

    return top;

}

/* 出栈 */

StackNode *popLinkStack(StackNode *top){

    int i = top->data;

    StackNode *p = top;

    top = top->next;

    free(p);

    printf("Pop: %d\n", i);

    return top;

}