/* 栈ADT链表实现的类型声明 */

struct Node;

typedef struct Ndoe *PtrToNode;

typedef PtrToNode Stack;

struct Node{

    ElementType Element;

    Stack Next;

};

/* 测试是否为空栈 */

int

IsEmpty( Stack S )

{

    return S->Next == NULL;

}

/* 创建空栈 */

Stack

CreateStack(void)

{

    Stack S;

    S = malloc(sizeof(struct Node));

    if(S == NULL)

        FatalError("no space");

    S->Next = NULL;

    return S;

}

/* 清空栈 */

/* 直接删除链表与无数次Pop异曲同工 */

void

MakeEmpty( Stack S)

{

    Stack p,TmpCell;

    p = S->Next;

    S->Next = NULL;

    while(p != NULL )

    {

        TmpCell = p->Next;

        free(p);

        p = TmpCell;

    }

}

/* 书上的实现方法 */

void

MakeEmpty( Stack S )

{

    if(S == NULL)

        Error("Must create a stack");

    else

    {

        while(!IsEmpty(S))

            Pop(S);

    }

}

/* Pop 例程 */

void

Pop( Stack S )

{

    PtrToNode FirstCell;

    FirstCelll = S->Next;

    S->Next = FirstCell->Next;

    free(FirstCell);

}

/* Push 进栈操作 */

void

Push( Stack S, ElementType X )

{

    PtrToNode TmpCell;

    TmpCell = malloc( sizeof( struct Node ) );

    if( TmpCell == NULL )

        FatalError("out of space");

    else

    {

        TmpCell->Element = X;

        TmpCell->Next = S->Next;

        S->Next = TmpCell;

    }

}

/* 返回栈顶元素 */

ElementType

Top( Stack S )

{

    if( IsEmpty( S ) )

        Fata

}