สอบถามการเขียนโปรแกรมภาษาซี โครงสร้างแบบต้นไม้ค่ะ

#include <stdio.h>
// #include<conio.h>
#include<stdlib.h>
#include<string.h>

typedef struct Tree Tree;

struct Tree 
{
  Tree * left, * right;
  int element;
};

Tree *make_empty(Tree *t)
{
  if (t != NULL)
  {
    make_empty(t->left);
    make_empty(t->right);
    free(t);
  }

  return NULL;
}

Tree *find_min(Tree *t)
{
  if (t == NULL)
  {
    return NULL;
  }
  else if (t->left == NULL)
  {
    return t;
  }
  else
  {
    return find_min(t->left);
  }
}

Tree *find_max(Tree *t)
{
  if (t == NULL)
  {
    return NULL;
  }
  else if (t->right == NULL)
  {
    return t;
  }
  else
  {
    return find_max(t->right);
  }
}

Tree *find(int elem, Tree *t)
{
  if (t == NULL)
  {
    return NULL;
  }

  if (elem < t->element)
  {
    return find(elem, t->left);
  }
  else if (elem > t->element)
  {
    return find(elem, t->right);
  }
  else
  {
    return t;
  }
}

                 
Tree * insert(int value, Tree * t) 
{
  Tree * new_node;
    
  if (t == NULL) 	// insert the first node
  {
    new_node = (Tree *) malloc (sizeof (Tree));
    if (new_node == NULL) 
    {
	    return t;
    }

    new_node->element = value;

	new_node->left = new_node->right = NULL;
	return new_node;
  }
  
  if (value < t->element) 		// less than
  {
    t->left = insert(value, t->left);
  } 
  else if (value > t->element) 	// greater than
  {
	  t->right = insert(value, t->right);
  } 
  else	// equal
  { 
    //duplicate, ignore it
	  return t;
  }
  return t;
}

Tree * deletenode(int value, Tree * t)
{
  
  Tree * x;
  Tree *tmp_cell;
  
  if (t==NULL) return NULL;
  
  if (value < t->element){
    t->left = deletenode(value, t->left);
  } 
  else if (value > t->element){
	t->right = deletenode(value, t->right);
  } 
  
  else if (t->left && t->right){	// case 1 (t:LR): t has both left and right children
    tmp_cell = find_min(t->right);
    t->element = tmp_cell->element;
    t->right = deletenode(t->element, t->right);
  }
  else{ 
    tmp_cell = t;
    if (t->left == NULL)			
      t = t->right;				       
    else if (t->right == NULL)		
      t = t->left;				   
    free(tmp_cell);
  }

  return t;
}




typedef struct asciinode_struct{
  struct asciinode_struct * left, * right;

  
  int edge_length;

  int height;

  int lablen;

  
  int parent_dir;

  
  char label[11];
} asciinode;


#define MAX_HEIGHT 1000
int lprofile[MAX_HEIGHT];
int rprofile[MAX_HEIGHT];
#define INFINITY (1<<20)


int gap = 3;


int print_next;

int MIN (int X, int Y)
{
  return ((X) < (Y)) ? (X) : (Y);
}

int MAX (int X, int Y)
{
  return ((X) > (Y)) ? (X) : (Y);
}

asciinode * build_ascii_tree_recursive(Tree * t)
{
  asciinode * node;

  if (t == NULL) return NULL;

  node = (asciinode *)malloc(sizeof(asciinode));
  node->left = build_ascii_tree_recursive(t->left);
  node->right = build_ascii_tree_recursive(t->right);

  if (node->left != NULL)
  {
    node->left->parent_dir = -1;
  }

  if (node->right != NULL)
  {
    node->right->parent_dir = 1;
  }

  sprintf(node->label, "%d", t->element);
  node->lablen = strlen(node->label);

  return node;
}


//Copy the tree into the ascii node structre
asciinode * build_ascii_tree(Tree * t)
{
  asciinode *node;
  if (t == NULL) return NULL;
  node = build_ascii_tree_recursive(t);
  node->parent_dir = 0;
  return node;
}

//Free all the nodes of the given tree
void free_ascii_tree(asciinode *node)
{
  if (node == NULL) return;
  free_ascii_tree(node->left);
  free_ascii_tree(node->right);
  free(node);
}


void compute_lprofile(asciinode *node, int x, int y)
{
  int i, isleft;
  if (node == NULL) return;
  isleft = (node->parent_dir == -1);
  lprofile[y] = MIN(lprofile[y], x-((node->lablen-isleft)/2));
  if (node->left != NULL)
  {
	  for (i=1; i <= node->edge_length && y+i < MAX_HEIGHT; i++)
    {
	    lprofile[y+i] = MIN(lprofile[y+i], x-i);
    }
  }
  compute_lprofile(node->left, x-node->edge_length-1, y+node->edge_length+1);
  compute_lprofile(node->right, x+node->edge_length+1, y+node->edge_length+1);
}

void compute_rprofile(asciinode *node, int x, int y)
{
  int i, notleft;
  if (node == NULL) return;
  notleft = (node->parent_dir != -1);
  rprofile[y] = MAX(rprofile[y], x+((node->lablen-notleft)/2));
  if (node->right != NULL)
  {
	  for (i=1; i <= node->edge_length && y+i < MAX_HEIGHT; i++)
    {
	    rprofile[y+i] = MAX(rprofile[y+i], x+i);
    }
  }
  compute_rprofile(node->left, x-node->edge_length-1, y+node->edge_length+1);
  compute_rprofile(node->right, x+node->edge_length+1, y+node->edge_length+1);
}


void compute_edge_lengths(asciinode *node)
{
  int h, hmin, i, delta;
  if (node == NULL) return;
  compute_edge_lengths(node->left);
  compute_edge_lengths(node->right);

  /* first fill in the edge_length of node */
  if (node->right == NULL && node->left == NULL)
  {
	  node->edge_length = 0;
  }
  else
  {
    if (node->left != NULL)
    {
	    for (i=0; i<node->left->height && i < MAX_HEIGHT; i++)
      {
		    rprofile[i] = -INFINITY;
	    }
	    compute_rprofile(node->left, 0, 0);
	    hmin = node->left->height;
    }
    else
    {
	    hmin = 0;
    }
	  if (node->right != NULL)
    {
	    for (i=0; i<node->right->height && i < MAX_HEIGHT; i++)
      {
		    lprofile[i] = INFINITY;
	    }
	    compute_lprofile(node->right, 0, 0);
	    hmin = MIN(node->right->height, hmin);
    }
    else
    {
	    hmin = 0;
    }
	  delta = 4;
	  for (i=0; i<hmin; i++)
    {
	    delta = MAX(delta, gap + 1 + rprofile[i] - lprofile[i]);
    }

   
	  if (((node->left != NULL && node->left->height == 1) ||
	      (node->right != NULL && node->right->height == 1))&&delta>4)
    {
      delta--;
    }

    node->edge_length = ((delta+1)/2) - 1;
  }

  
  h = 1;
  if (node->left != NULL)
  {
	  h = MAX(node->left->height + node->edge_length + 1, h);
  }
  if (node->right != NULL)
  {
	  h = MAX(node->right->height + node->edge_length + 1, h);
  }
  node->height = h;
}


void print_level(asciinode *node, int x, int level)
{
  int i, isleft;
  if (node == NULL) return;
  isleft = (node->parent_dir == -1);
  if (level == 0) 
  {
	  for (i=0; i<(x-print_next-((node->lablen-isleft)/2)); i++) 
    {
	    printf(" ");
    }
	  print_next += i;
	  printf("%s", node->label);
	  print_next += node->lablen;
  } 
  else if (node->edge_length >= level) 
  {
	  if (node->left != NULL) 
    {
	    for (i=0; i<(x-print_next-(level)); i++) 
      {
		    printf(" ");
	    }
	    print_next += i;
	    printf("/");
	    print_next++;
    }
	  if (node->right != NULL) 
    {
	    for (i=0; i<(x-print_next+(level)); i++) 
      {
		    printf(" ");
	    }
	    print_next += i;
	    printf("\\");
	    print_next++;
    }
  } 
  else 
  {
	  print_level(node->left, 
                x-node->edge_length-1, 
                level-node->edge_length-1);
	  print_level(node->right, 
                x+node->edge_length+1, 
                level-node->edge_length-1);
  }
}


void print_ascii_tree(Tree * t) 
{
  asciinode *proot;
  int xmin, i;
  if (t == NULL) return;
  proot = build_ascii_tree(t);
  compute_edge_lengths(proot);
  for (i=0; i<proot->height && i < MAX_HEIGHT; i++) 
  {
	  lprofile[i] = INFINITY;
  }
  compute_lprofile(proot, 0, 0);
  xmin = 0;
  for (i = 0; i < proot->height && i < MAX_HEIGHT; i++) 
  {
	  xmin = MIN(xmin, lprofile[i]);
  }
  for (i = 0; i < proot->height; i++) 
  {
	  print_next = 0;
	  print_level(proot, -xmin, i);
	  printf("\n");
  }
  if (proot->height >= MAX_HEIGHT) 
  {
	  printf("(This tree is taller than %d, and may be drawn incorrectly.)\n", MAX_HEIGHT);
  }
  free_ascii_tree(proot); 
}

Tree* initialTree(Tree *root){
  int treeData[] = {20, 12, 30, 15, 40, 10, 25};
  int value;

 
  int sizeOfTree = sizeof(treeData)/sizeof(treeData[0]);
  for(int i = 0; i < sizeOfTree; i++){
    value = treeData[i];
	root = insert(value, root);
  }
  print_ascii_tree(root);
  return root;
}


int main() 
{
  
  
  Tree * root;
  int i;
  int value;
  int select;
  root = NULL;
  
  // clrscr();
  make_empty(root);
  
  root = initialTree(root);

  do{
    printf("\n\nMENU: 1: Insert, 2: Delete, 3: Undo, 4. History 5: Exit\n");
    printf("Select: ");
    fflush(stdin);
    scanf("%d", &select);
    switch(select){
      case 1: printf("Insert value: ");
		scanf("%d", &value);
		root = insert(value, root);
		print_ascii_tree(root);


		// <<  AddHistory code  >>

		break;
      case 2: printf("Delete value: ");
		scanf("%d", &value);
		root = deletenode(value, root);
		print_ascii_tree(root);

		// << AddHistory code  >>

		break;
      case 3: printf("Undo: ");

        // << UNDO code >>

		print_ascii_tree(root);
		break;
      case 4: printf("History: \n");

        // <<  ViewHistory code  >>

		break;
      default:  break;
    }
  }while(select != 5);

  make_empty(root);
  return 0;
}