struct BTNode { 
  char data; 
  struct BTNode* pLChild; 
  struct BTNode* pRChild; 
}; 

struct BTNode* create_list() { 
 
  struct BTNode* pA = (struct BTNode*)malloc(sizeof(BTNode)); 
  struct BTNode* pB = (struct BTNode*)malloc(sizeof(BTNode)); 
  struct BTNode* pC = (struct BTNode*)malloc(sizeof(BTNode)); 
  struct BTNode* pD = (struct BTNode*)malloc(sizeof(BTNode)); 
  struct BTNode* pE = (struct BTNode*)malloc(sizeof(BTNode)); 
   
  pA->data = 'A'; 
  pB->data = 'B'; 
  pC->data = 'C'; 
  pD->data = 'D'; 
  pE->data = 'E';  
 
  pA->pLChild = pB; 
  pA->pRChild = pC; 
  pB->pLChild = pB->pRChild = NULL; 
 
  pC->pLChild = pD; 
  pC->pRChild = NULL; 
 
  pD->pLChild = NULL; 
  pD->pRChild = pE; 
 
  pE->pLChild = pE->pRChild = NULL; 
 
  return pA; 
} 

//先序输出 
void PreTravense(struct BTNode* pHead) { 
  if (NULL!= pHead) 
  { 
    printf("%c", pHead->data); 
    if (NULL!= pHead->pLChild) 
    { 
      PreTravense(pHead->pLChild); 
    } 
    if (NULL != pHead->pRChild) 
    { 
      PreTravense(pHead->pRChild); 
    } 
  } 
} 

//中序输出 
void InTravense(struct BTNode* pHead) { 
  if (NULL != pHead) 
  { 
    if (NULL != pHead->pLChild) 
    { 
      PreTravense(pHead->pLChild); 
    } 
    printf("%c", pHead->data); 
     
    if (NULL != pHead->pRChild) 
    { 
      PreTravense(pHead->pRChild); 
    } 
  } 
} 

//后序输出 
void PostTravense(struct BTNode* pHead) { 
  if (NULL != pHead) 
  { 
    if (NULL != pHead->pLChild) 
    { 
      PreTravense(pHead->pLChild); 
    }    
 
    if (NULL != pHead->pRChild) 
    { 
      PreTravense(pHead->pRChild); 
    } 
    printf("%c", pHead->data); 
  } 
} 

int main() { 
  printf("创建序列\n"); 
  struct BTNode* pHead = create_list(); 
 
  printf("先序输出\n"); 
  PreTravense(pHead); 
  printf("中序输出\n"); 
  InTravense(pHead); 
  printf("后序输出\n"); 
  PostTravense(pHead); 
  return 0; 
}