4-7 在一个数组中实现两个堆栈 (20分)

#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 */

Stack CreateStack(int MaxSize) {
Stack S;
S = (Stack)malloc(sizeof(struct SNode));
S->MaxSize = MaxSize;
S->Data = (ElementType*)malloc(MaxSize*sizeof(ElementType));
S->Top1 = -1;
S->Top2 = MaxSize;
return S;
}

bool Push(Stack S, ElementType X, int Tag) {
if (S == NULL)
return false;
if (S->Top2 - S->Top1 == 1) {
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 ERROR;
if (Tag == 1) {
if (S->Top1 == -1) {
printf("Stack 1 Empty\n");
return ERROR;
}
else
return S->Data[(S->Top1)--];
}

if (Tag == 2) {
if (S->Top2 == S->MaxSize) {
printf("Stack 2 Empty\n");
return ERROR;
}
else
return S->Data[(S->Top2)++];
}
}