Space shared by two stacks

#include <stdio.h>
#include <malloc.h>

#define MAXSIZE 20

typedef int T;
typedef struct DoubleStack
{
    
	T data[MAXSIZE];
	int top1;// head 
	int top2;// tail 
}*dostack;

bool InitStack(dostack s)// initialization 
{
    
	if (!s)
		return false;
	s->top1 = 0;
	s->top2 = MAXSIZE - 1;
	return true;
}

bool ClearStack(dostack s)// Clear the stack 
{
    
	if (!s)
		return false;
	s->top1 = 0;
	s->top2 = MAXSIZE - 1;
	return true;
}

bool Is_Empty(dostack s)// Sentenced to empty 
{
    
	if (s->top1 == 0 && s->top2 == MAXSIZE - 1)
		return true;
	else return false;
}

bool Is_Full(dostack s)// Full sentence 
{
    
	if (s->top1 + 1 == s->top2)
		return true;
	else return false;
}

int GetLength(dostack s)// The number of data 
{
    
	return s->top1 + MAXSIZE - s->top2;
}

bool Push(dostack s, T val, int num)// Select stack ,1 To the left ,2 For the right 
{
    
	if (Is_Full(s))
		return false;
	if (num == 1)
	{
    
		s->data[s->top1++] = val;
	}
	else if (num == 2)
	{
    
		s->data[s->top2--] = val;
	}
	else false;
	return true;
}

T Pop(dostack s,int num)// Select stack ,1 Bit left ,2 For the right 
{
    
	if (Is_Empty(s))
		return -1;
	T tmp;
	if (num == 1)
	{
    
		if (s->top1 == 0)
			return -1;
		tmp = s->data[--s->top1];
	}
	else if (num == 2)
	{
    
		if (s->top2 == MAXSIZE - 1)
			return -1;
		tmp = s->data[++s->top2];
	}
	else return -1;
	return tmp;
}

T GetVal(dostack s, int num)// Get the desired position stack top element 
{
    
	if (Is_Empty(s))
		return -1;
	T tmp;
	if (num == 1)
	{
    
		if (s->top1 == 0)
			return -1;
		tmp = s->data[s->top1];
	}
	else if (num == 2)
	{
    
		if (s->top2 == MAXSIZE - 1)
			return -1;
		tmp = s->data[s->top2];
	}
	else return -1;
	return tmp;
}

void Show(dostack s)// Traverse 
{
    
	int i = 0;
	while (i < s->top1)
	{
    
		printf("%d ", s->data[i++]);
	}
	printf("\t");
	i = s->top2 + 1;
	while (i < MAXSIZE)
	{
    
		printf("%d ", s->data[i++]);
	}
	printf("\n");
}

int main()
{
    
	dostack s;
	s = (dostack)malloc(sizeof(dostack));
	InitStack(s);
	for (int i = 1; i <= 5; i++)
	{
    
		Push(s, i, 1);
		Push(s, i, 2);
	}
	Show(s);
	printf("%d\t", Pop(s, 1));
	printf("%d\n", Pop(s, 2));
	Show(s);
	return 0;
}