Language: C

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

typedef struct{
  int key;
  Node *next, *prev;
} Node;

Node *nil;

Node* listSearch(int key){
  Node *cur = nil->next;
  while (cur != nil && cur->key != key){
    cur - cur->next;
  }
  return cur;
}

void iii(void) {
  nil = (Node *)malloc(sizeof(Node));
  nil->next = nil;
  nil->prev = nil;
}

void plist(void){
  Node *cur = nil->next;
  int isf = 0;
  while(1){
    if(cur==nil)break;
    if(isf++>0)
      printf(" ");
    printf("%d", cur->key);
    cur = cur->next;
  }
  printf("\n");
}

void ddd(Node *t){
  if(t==nil) return;
  t->prev->next = t->next;
  t->next->prev = t->prev;
  free(t);
}

void insert(int key){
  Node *x = (Node *)malloc(sizeof(Node));
  x->key = key;
  x->next = nil-next;
  nil->next->prev -> x;
  nil->next = x;
  x->prev = nil;
}

int main(){
  int key, n, i;
  int size = 0, np=0, nd=0;
  char com[20];

  scanf("%d",&n);
  iii();
  for(i=0; i<n; i++){
    scanf("%s%d", com, &key);
    if(com[0]=='i'){
      insert(key);
      np++;
      size++;
    } else if (com[0]=='d'){
      if(strlen(com)>6){
        if(com[6]=='F')
          ddd(nil->next);
        else if(com[6]=='L')
          ddd(nil->prev);
      } else {
        ddd(listSearch(key));
        nd++;
      }
      size--;
    }
  }
  plist();
  return 0;
}

Compiler output:
main.c:7:3: error: unknown type name 'Node'
    7 |   Node *next, *prev;
      |   ^~~~
main.c: In function 'listSearch':
main.c:13:15: error: initialization of 'Node *' from incompatible pointer type 'int *' [-Wincompatible-pointer-types]
   13 |   Node *cur = nil->next;
      |               ^~~
main.c:15:9: error: invalid operands to binary - (have 'Node *' and 'int *')
   15 |     cur - cur->next;
      |         ^ ~~~~~~~~~
      |              |
      |              int *
main.c: In function 'iii':
main.c:22:13: error: assignment to 'int *' from incompatible pointer type 'Node *' [-Wincompatible-pointer-types]
   22 |   nil->next = nil;
      |             ^
main.c:23:13: error: assignment to 'int *' from incompatible pointer type 'Node *' [-Wincompatible-pointer-types]
   23 |   nil->prev = nil;
      |             ^
main.c: In function 'plist':
main.c:27:15: error: initialization of 'Node *' from incompatible pointer type 'int *' [-Wincompatible-pointer-types]
   27 |   Node *cur = nil->next;
      |               ^~~
main.c:34:9: error: assignment to 'Node *' from incompatible pointer type 'int *' [-Wincompatible-pointer-types]
   34 |     cur = cur->next;
      |         ^
main.c: In function 'ddd':
main.c:41:10: error: request for member 'next' in something not a structure or union
   41 |   t->prev->next = t->next;
      |          ^~
main.c:42:10: error: request for member 'prev' in something not a structure or union
   42 |   t->next->prev = t->prev;
      |          ^~
main.c: In function 'insert':
main.c:49:17: error: 'next' undeclared (first use in this function)
   49 |   x->next = nil-next;
      |                 ^~~~
main.c:49:17: note: each undeclared identifier is reported only once for each function it appears in
main.c:50:12: error: request for member 'prev' in something not a structure or union
   50 |   nil->next->prev -> x;
      |            ^~
main.c:51:13: error: assignment to 'int *' from incompatible pointer type 'Node *' [-Wincompatible-pointer-types]
   51 |   nil->next = x;
      |             ^
main.c:52:11: error: assignment to 'int *' from incompatible pointer type 'Node *' [-Wincompatible-pointer-types]
   52 |   x->prev = nil;
      |           ^
main.c: In function 'main':
main.c:71:18: error: passing argument 1 of 'ddd' from incompatible pointer type [-Wincompatible-pointer-types]
   71 |           ddd(nil->next);
      |               ~~~^~~~~~
      |                  |
      |                  int *
main.c:39:16: note: expected 'Node *' but argument is of type 'int *'
   39 | void ddd(Node *t){
      |          ~~~~~~^
main.c:73:18: error: passing argument 1 of 'ddd' from incompatible pointer type [-Wincompatible-pointer-types]
   73 |           ddd(nil->prev);
      |               ~~~^~~~~~
      |                  |
      |                  int *
main.c:39:16: note: expected 'Node *' but argument is of type 'int *'
   39 | void ddd(Node *t){
      |          ~~~~~~^