트리 // 재귀함수

# include <stdio.h>
# include <stdlib.h>
# define _AND_ &&
# define _ERROR_ 1
typedef struct _Node {
 int data;
 struct _Node* left_n;
 struct _Node* right_n;
}Node;
Node* root = NULL;
// ++++++++++++++++++++++++++++++++++++++++
void initTree(int paramNum);
Node* AddChildNode(Node* pNode, int data);
void PreOrder(Node *Proot);
// ++++++++++++++++++++++++++++++++++++++++
int main(void) {
 initTree(1); // 최상위 노드
 Node* Leftnode = NULL;
 Node* Rightnode = NULL;
 Leftnode = AddChildNode(root, 2);
 Rightnode = AddChildNode(root, 3);
 AddChildNode(Leftnode, 4);
 PreOrder(root);
 printf("\n");
 return 0;
} // end of main function
void initTree(int paramNum) {
 Node* retNode = NULL;
 retNode = (Node*)malloc(sizeof(Node));
 if (retNode == NULL) {
  exit(_ERROR_);
 }
 else {
  //retNode != NULL
  retNode->data = paramNum;
  retNode->left_n = NULL;
  retNode->right_n = NULL;
  root = retNode;
 }
} // end of initTree function
Node* AddChildNode(Node* pNode, int data) {
 if (pNode->left_n != NULL _AND_ pNode->right_n != NULL) {
  printf("child node full ... !!!\n");
  exit(_ERROR_);
 }
 else {
  //pNode->left_n == NULL OR pNode->right_n == NULL
  if (pNode->left_n == NULL) {
   // LEFT CHILD
   Node* L_Child = (Node*)malloc(sizeof(Node));
   if (L_Child == NULL) {
    printf("left_child malloc error ... !!!\n");
    exit(_ERROR_);
   }
   else { // L_Child != NULL
    L_Child->left_n  = NULL;
    L_Child->right_n = NULL;
    L_Child->data = data;
    pNode->left_n = L_Child;
    return L_Child;
   }
  }
  else {
   // pNode->left_n != NULL
   // RIGHT CHILD
   Node* R_Child = (Node*)malloc(sizeof(Node));
   if (R_Child == NULL) {
    printf("right_child malloc error ... !!!\n");
    exit(_ERROR_);
   }
   else { // R_Child != NULL
    R_Child->left_n = NULL;
    R_Child->right_n = NULL;
    R_Child->data = data;
    pNode->right_n = R_Child;
    return R_Child;
   }
  }
 }
} // end of AddChildNode function
void PreOrder(Node *Proot) {
 printf("%d [%#x]  ", Proot->data, Proot);
 if (Proot->left_n) { PreOrder(Proot->left_n); }
 if (Proot->right_n) { PreOrder(Proot->right_n); }
} // end of PreOrder function