Language: C

#include<stdio.h>
#include<stdlib.h>

struct node{
  struct node *right;
  struct node *left;
  struct node *parent;
  int key;
};
typedef struct node * Node;
#define NIL NULL

Node root;

Node treeMinimum(Node x){
  while(x->left!=NIL){
    x=x->left;
  }
  return x;
}

Node treeSearch(Node u, int k){
  if(u==NIL || k==u->key) return u;
  if(k < u->key){ return treeSearch(u->left,k);}
  else { return treeSearch(u->right,k);}
}

Node treeSuccessor(Node x){
  Node y;
  if(x->right!=NIL) return treeMinimum(x->right);
  y=x->parent;
  while(y!=NIL && x==y->right){
    x=y;
    y=y->parent;
  }
  return y;
}

Node treeDelete(Node z){
  Node y; // node to be deleted
  Node x; // child of y
  if(z->left==NIL || z->right==NIL){ y=z;}
  else {y= treeSuccessor(z);}
  if(y->left!=NIL){ x=y->left;}
  else {x=y->right;}
  if(x!=NIL){ x->parent=y->parent;}
  if(y->parent==NIL){ root=x;}
  else if(y==y->parent->left){ y->parent->left=x;}
  else {y->parent->right=x;}
  if(y!=z){
    z->key=y->key;
    /*z->left=y->left;
    z->right=y->right;
    z->parent=y->parent;*/
  }
    return y;
}


void insert(int k){
  Node y = NIL;
  Node x = root;
  Node z;

  z = malloc(sizeof(struct node));
  z->key = k;
  z->left = NIL;
  z->right = NIL;
  //printf("%d\n",x->key);
  while(x!=NIL){
    y=x;
    if(z->key < x->key){ x=x->left;}
    else{x=x->right;}
  }
  z->parent=y;
  if(y==NIL){ root = z;}
  else if(z->key < y->key){y->left=z;}
  else y->right=z;
}

void inorder(Node u){
  if(u!=NIL){
    inorder(u->left);
    printf(" %d",u->key);
    inorder(u->right);
  }
}
void preorder(Node u){
  if(u!=NIL){
    printf(" %d",u->key);
    preorder(u->left);
    preorder(u->right);
  }
}

Node * find(Node *u, int k){
  while(u!=NIL && k!=u->key){
    if(k<u->key) u=u->left;
    else u=u->right;
  }
  return u;
}

int main(){
  int n, i, x;
  char com[20];
  scanf("%d", &n);
  root=NIL;
  for ( i = 0; i < n; i++ ){
    scanf("%s", com);
    if ( com[0] == 'f' ){
      scanf("%d", &x);
      Node t = treeSearch(root, x);
      if ( t != NIL ) printf("yes\n");
      else printf("no\n");
    } else if ( com[0] == 'i' ){
      scanf("%d", &x);
      insert(x);
    } else if ( com[0] == 'p' ){
      inorder(root);
      printf("\n");
      preorder(root);
      printf("\n");
    } else if ( com[0] == 'd' ){
      scanf("%d", &x);
      treeDelete(treeSearch(root, x));
    }
  }

  return 0;
}

Compiler output:
main.c: In function 'find':
main.c:97:23: error: 'u' is a pointer to pointer; did you mean to dereference it before applying '->' to it?
   97 |   while(u!=NIL && k!=u->key){
      |                       ^~
      |                      -
      |                      (*u)
main.c:98:11: error: 'u' is a pointer to pointer; did you mean to dereference it before applying '->' to it?
   98 |     if(k<u->key) u=u->left;
      |           ^~
      |          -
      |          (*u)
main.c:98:21: error: 'u' is a pointer to pointer; did you mean to dereference it before applying '->' to it?
   98 |     if(k<u->key) u=u->left;
      |                     ^~
      |                    -
      |                    (*u)
main.c:99:13: error: 'u' is a pointer to pointer; did you mean to dereference it before applying '->' to it?
   99 |     else u=u->right;
      |             ^~
      |            -
      |            (*u)