6-7 在一个数组中实现两个堆栈 (20分)

Stack CreateStack( int MaxSize );
bool Push( Stack S, ElementType X, int Tag );
ElementType Pop( Stack S, int Tag );

typedef int Position;
struct SNode {
    ElementType *Data;
    Position Top1, Top2;
    int MaxSize;
};
typedef struct SNode *Stack;

#include <stdio.h>
#include <stdlib.h>

#define ERROR 1e8
typedef int ElementType;
typedef enum { push, pop, end } Operation;
typedef enum { false, true } bool;
typedef int Position;
struct SNode {
    ElementType *Data;
    Position Top1, Top2;
    int MaxSize;
};
typedef struct SNode *Stack;

Stack CreateStack( int MaxSize );
bool Push( Stack S, ElementType X, int Tag );
ElementType Pop( Stack S, int Tag );

Operation GetOp();  /* details omitted */
void PrintStack( Stack S, int Tag ); /* details omitted */

int main()
{
    int N, Tag, X;
    Stack S;
    int done = 0;

    scanf("%d", &N);
    S = CreateStack(N);
    while ( !done ) {
        switch( GetOp() ) {
        case push: 
            scanf("%d %d", &Tag, &X);
            if (!Push(S, X, Tag)) printf("Stack %d is Full!\n", Tag);
            break;
        case pop:
            scanf("%d", &Tag);
            X = Pop(S, Tag);
            if ( X==ERROR ) printf("Stack %d is Empty!\n", Tag);
            break;
        case end:
            PrintStack(S, 1);
            PrintStack(S, 2);
            done = 1;
            break;
        }
    }
    return 0;
}

/* 你的代码将被嵌在这里 */

5
Push 1 1
Pop 2
Push 2 11
Push 1 2
Push 2 12
Pop 1
Push 2 13
Push 2 14
Push 1 3
Pop 2
End

Stack 2 Empty
Stack 2 is Empty!
Stack Full
Stack 1 is Full!
Pop from Stack 1: 1
Pop from Stack 2: 13 12 11

Stack CreateStack( int MaxSize )
{
    Stack stack=(Stack)malloc(sizeof(struct SNode));
    stack->Data=(int *)malloc(sizeof(ElementType)*MaxSize);
    stack->Top1=-1;
    stack->Top2=MaxSize;
    stack->MaxSize=MaxSize;
    return stack;
}
bool Push( Stack S, ElementType X, int Tag )
{
    if(S==NULL)
        return false;
    if(S->Top1+1==S->Top2){
        printf("Stack Full\n");
        return false;
    }
    if(Tag==1)
        S->Data[++S->Top1]=X;
    else
        S->Data[--S->Top2]=X;
    return true;
}
ElementType Pop( Stack S, int Tag )
{
    if(S==NULL)
        return false;
    if(Tag==1)
    {
        if(S->Top1==-1)
        {
            printf("Stack %d Empty\n",Tag);
            return ERROR;
        }
        return S->Data[S->Top1--];
    }
    if(Tag==2)
    {
        if(S->Top2==S->MaxSize)
        {
            printf("Stack %d Empty\n",Tag);
            return ERROR;
        }
        return S->Data[S->Top2++];
    }
}