大家给看一下，C的堆栈的有关问题

/*动态堆栈程序*/
#include<stdio.h>
#include<stdlib.h>

struct stackNode {  /*自引用结构*/
int data;
struct stackNode *nextPtr;
};

typedef struct stackNode STSCKNODE;
typedef STSCKNODE *STSCKNODEPTR;
void push(STSCKNODEPTR *,int);
int pop(STSCKNODEPTR *);
int isEmpty(STSCKNDOEPTR);
void printStack(STSCKNODEPTR);
void instructions(void);

void main()
{
  STSCKNODEPTR stackPtr=NULL; /*指向栈顶*/
  int choice,value;

  instructions();
  printf("?");
  scanf("%d",&choice);
  
  while(choice!=3) {
   switch(choice) {
    case 1:  /*把值压入堆栈*/
     printf("Enter an integer:");
     scanf("%d",&value);
     push(&stackPtr,value);
     printStack(stackPtr);
     break;
    case 2:
     if (!isEmpty(stackPtr))
      printf("The popped value is %d.\n",pop(&stackPtr));
      printStack(stackPtr);
      break;
    default:
     printf("Invalid choice:\n\n");
     instructions();
     break;
                  }
   printf("?");
   scanf("%d",&choice);
                   }
   printf("End of run.\n");
}

/*打印菜单指令*/
void instructions(void)
{
  printf("Enter choice:\n"
        "1 to push a vlaue on the stack\n"
        "2 to pop a value of the stack\n"
        "3 to end program.\n");
}

/*在栈顶插入一个结点*/
void push(STACKNODEPTR * topPtr,int info)
{
  STACKNODEPTR newPtr;
  
  newPtr=malloc(sizeof(STACKNODE));
  
  if(newPtr!=NULL) {
    newPtr.data=info;
    newPtr.nextPtr=*topPtr;
    *topPtr=newPtr;
                   }
   else
    printf("%d not inserted.No memory available.\n",info);
}

/*删除栈顶结点*/
int pop(STACKNODEPTR *topPtr)
{
  STACKNODEPTR tempPtr;
  int popValue;
  
  tempPtr=*topPtr;
  popValue=(*topPtr).data;
  *topPtr=(*topPtr).nextPtr;
  free(tempPtr);
  return popValue;
}

/*打印堆栈*/
void printStack(STACKNODEPTR currentPtr)
{
  if (currentPtr==NULL)
   printf("The stack is empty.\n\n");
  else {
   printf("The stack is:\n");
   while(currentPtr!=NULL) {
     printf("%d-->",currentPtr.data);
     currentPtr=currentPtr.nextPtr;
     
                           }
    printf("NULL\n");
       }
}

/*堆栈为空*/
int isEmpty(STACKNODEPTR topPtr)
{
  return topPtr==NULL;
}