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


 
int main(){
  int n, i, y;
  char com[20];
  scanf("%d", &n);
   
  for ( i = 0; i < n; i++ ){
    scanf("%s", com);
    if ( com[0] == 'f' ){
      scanf("%d", &y);
      Node t = treeSearch(root, y);
      if ( t != NIL ) printf("yes\n");
      else printf("no\n");
    } else if ( com[0] == 'i' ){
      scanf("%d", &x);
      insert(y);
    } else if ( com[0] == 'p' ){
      inorder(root);
      printf("\n");
      preorder(root);
      printf("\n");
    } else if ( com[0] == 'd' ){
      scanf("%d", &y);
      treeDelete(treeSearch(root, y));
    }
  }
  return 0;
}
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;
   
  while(x != NIL){
    y = x;
     
    if(k < 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 ->left != NIL) {
    inorder(u->left);
    printf(" %d",u->key);
  }
   
  else printf(" %d",u->key);
   
  if(u->right != NIL) inorder(u->right);
}
 void treeDelete(Node z){
  Node x; // node to be deleted
  Node y; // child of y
 
  if(z->left == NIL || z->right == NIL) x = z;
  else x = treeSuccessor(z);
   
  if(x->left != NIL) y = x->left;
  else y = x->right;
   
  if(y != NIL) y->parent = x->parent;
  if(x->parent == NIL) root = y;
  else if(x == x->parent->left) x->parent->left = y;
  else x->parent->right = y;
   
  if(x != z) z->key = x->key;
   
}
 
void preorder(Node u){
  printf(" %d",u->key);
   
  if(u->left != NIL) preorder(u->left);
  if(u->right != NIL) preorder(u->right);
}
 

Compiler output:
main.c: In function 'treeMinimum':
main.c:18:5: error: 'x' undeclared (first use in this function)
   18 |     x = y->left;
      |     ^
main.c:18:5: note: each undeclared identifier is reported only once for each function it appears in
main.c: In function 'main':
main.c:60:20: error: 'x' undeclared (first use in this function)
   60 |       scanf("%d", &x);
      |                    ^
main.c:61:7: error: implicit declaration of function 'insert' [-Wimplicit-function-declaration]
   61 |       insert(y);
      |       ^~~~~~
main.c:63:7: error: implicit declaration of function 'inorder' [-Wimplicit-function-declaration]
   63 |       inorder(root);
      |       ^~~~~~~
main.c:65:7: error: implicit declaration of function 'preorder' [-Wimplicit-function-declaration]
   65 |       preorder(root);
      |       ^~~~~~~~
main.c:69:7: error: implicit declaration of function 'treeDelete' [-Wimplicit-function-declaration]
   69 |       treeDelete(treeSearch(root, y));
      |       ^~~~~~~~~~
main.c: At top level:
main.c:74:6: warning: conflicting types for 'insert'; have 'void(int)'
   74 | void insert(int k){
      |      ^~~~~~
main.c:61:7: note: previous implicit declaration of 'insert' with type 'void(int)'
   61 |       insert(y);
      |       ^~~~~~
main.c:97:6: warning: conflicting types for 'inorder'; have 'void(struct node *)'
   97 | void inorder(Node u){
      |      ^~~~~~~
main.c:63:7: note: previous implicit declaration of 'inorder' with type 'void(struct node *)'
   63 |       inorder(root);
      |       ^~~~~~~
main.c:108:7: warning: conflicting types for 'treeDelete'; have 'void(struct node *)'
  108 |  void treeDelete(Node z){
      |       ^~~~~~~~~~
main.c:69:7: note: previous implicit declaration of 'treeDelete' with type 'void(struct node *)'
   69 |       treeDelete(treeSearch(root, y));
      |       ^~~~~~~~~~
main.c:127:6: warning: conflicting types for 'preorder'; have 'void(struct node *)'
  127 | void preorder(Node u){
      |      ^~~~~~~~
main.c:65:7: note: previous implicit declaration of 'preorder' with type 'void(struct node *)'
   65 |       preorder(root);
      |       ^~~~~~~~