#include 
   
   
    
    
#include 
    
    
     
     
#include 
     
     
      
      

#ifndef ERROR
#define ERROR (0)
#endif
#ifndef OK
#define OK	(!ERROR)
#endif

#define STACK_INIT_SIZE 100
#define STACKINCREMENT  10

typedef	int SElemType;
typedef struct SqStack{
	SElemType	*base;	
	SElemType	*top;	
	int			stacksize;
}SqStack, *pStack;
pStack S;

pStack InitStack(pStack S)
{
	S = (pStack)malloc(STACK_INIT_SIZE * sizeof(SElemType));
	if(S == NULL){
		return ERROR;
	}
	S->base = (SElemType *)S;
	S->top = S->base;
	S->stacksize = STACK_INIT_SIZE;

	return S;
}

pStack Push(pStack S, SElemType e)
{
	if((S->top - S->base) >= S->stacksize){
		S->base = (SElemType *)realloc(S, (S->stacksize + STACKINCREMENT)*sizeof(SElemType));
		if(S->base == NULL)	
				return ERROR;
		S->top = S->base + S->stacksize;
		S->stacksize += STACKINCREMENT;
	}
	*S->top++ = e;
	return S;
}

SElemType GetTop(pStack S)
{
	if(S->top == S->base)
			return ERROR;
	return *(S->top - 1);
}

SElemType Pop(pStack S)
{
	if(S->top == S->base)
			return 0;
	return *(--S->top);
}

int GetLength(pStack S)
{
	int length = 0;
	if(S->top == S->base)
			return 0;

	while(S->top-- != S->base)
			length++;
	return length;
}

int
main(void)
{
	int 	length;
	SElemType	elm;
	
	S = InitStack(S);

	S = Push(S, 3);
	S = Push(S, 4);
	S = Push(S, 6);

	elm = GetTop(S);
	printf("the top element of stack S is : %d.\n", elm);

	elm = Pop(S);
	printf("the top element of stack S is : %d.\n", elm);

	elm = Pop(S);
	printf("the top element of stack S is : %d.\n", elm);

	S = Push(S, 7);
	S = Push(S, 8);

	length = GetLength(S);
	printf("the length of stack S is %d.\n", length);

	free(S);
	return 0;
}