typedef char ElemType;

typedef struct LkStackNode{

    ElemType data;

    LkStackNode *next;

}*Stack,SNode,*PNode;

Stack IntiStack(){

    Stack s;

    s=new LkStackNode;  //分配结点空间

    s->next=NULL;         //处理next指针 

    return s;                  //返回栈指针

}

bool Push(Stack S,ElemType &x){

    if(S==NULL){

        return false;   //栈无效，返回false

    }

    PNode FirstCell;

    FirstCell=new SNode;  //为待数据分配一个结点空间 

    FirstCell->data=x;

    FirstCell->next=S->next;  //将新结点插在数据结点的最前面

    S->next=FirstCell;

    return true;

}

bool Pop(Stack S,ElemType &x){

    if(S==NULL||S->next==NULL){   //栈无效或空栈，无法出栈，返回false

        return false;

    }

    PNode FirstCell;

    FirstCell=S->next;

    x=FirstCell->data;         //返回栈顶元素 

    S->next=FirstCell->next;

    delete FirstCell;          //释放栈顶空间

    return true;

}

bool Top(Stack S,ElemType &x){

    if(S==NULL||S->next==NULL){   //栈无效或空栈

        return false;

    }

    x=S->next->data;

    return true;

}