This problem requires two stacks in an array.

Function interface definition:

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

Where Tag is the Stack number, take 1 or 2; MaxSize Stack array size; the Stack structure is defined as follows:

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

Note: if the stack is full, the Push function must output "Stack Full" and return false; if a stack is empty, the Pop function must output "Stack Tag Empty" (where Tag is the number of the stack) and return ERROR.

Sample referee test procedure:

#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;
}

/* Your code will be embedded here */

Input example:

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

Output example:

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