Language: C++

#include<iostream>
using namespace std;

class Node{
	public:
		Node* prev;
		Node* next;
		int data;
		Node(){
			prev=0;
			next=0;
			data=0;
		}
};

class List{
	private:
		Node head;
	public:
		LinkedList(){
			head.prev=&head;
			head.next=&head;
		}
		int inseart(int x);
		int del(int x);
		int deleteFirst();
		int deleteLast();
		void print();
};

int List::insert(int x){
	Node* p=new Node();
	if(p==0){
		return -1;
	}
	Node* q=&head;
	Node* r=&head.next;
	p->prev=q;
	p->next=r;
	p->data=x;
	q->next=p;
	r->prev=p;
	return 0;
}

int List::del(int x){
	Node* p;
	for(p=head.next;p!=&head;p=p->next){
		if(p->data==x){
			break;
		}
	}
	if(p==&head){
		return -2;
	}
	Node* q=p->prev;
	Node* r=p->next;
	q->next=r;
	r->prev=q;
	delete p;
	return 0;
}

int List::deleteFirst(){
	Node* p=head.next;
	if(p==&head){
		return -2;
	}
	Node* q=p->prev;
	Node* r=p->next;
	q->next=r;
	r->prev=q;
	delete p;
	return 0;
}
	
int List::deleteLast(){
	Node* p=head.prev;
	if(p==&head){
		return -2;
	}
	Node* q=p->prev;
	Node* r=p->next;
	q->next=r;
	r->prev=q;
	delete p;
	return 0;
}

void List::print(){
	for(Node* p=head.next;p!=head;p=p->next){
		cout<<p->data;
		if(p->next!=&head){
			cout<<' ';
		}else{
			cout<<endl;
		}
	}
}

int main(){
	List L;
	int n;
	cin>>n;
	for(int i=0;i<n;i++){
		char com[20];
		cin>>com;
		if(com[0]=='i'){
			int x;
			cin>>x;
			L.insert(x);
		}else if(com[6]=='F'){
			L.deleteFirst();
		}else if(com[6]=='L'){
			L.deleteLast();
		}else{
			int x;
			cin>>x;
			L.del(x);
		}
	}
	L.print();

	return 0;
}

Compiler output:
a.cc:20:17: error: ISO C++ forbids declaration of 'LinkedList' with no type [-fpermissive]
   20 |                 LinkedList(){
      |                 ^~~~~~~~~~
a.cc: In member function 'int List::LinkedList()':
a.cc:23:17: warning: no return statement in function returning non-void [-Wreturn-type]
   23 |                 }
      |                 ^
a.cc: At global scope:
a.cc:31:5: error: no declaration matches 'int List::insert(int)'
   31 | int List::insert(int x){
      |     ^~~~
a.cc:31:5: note: no functions named 'int List::insert(int)'
a.cc:16:7: note: 'class List' defined here
   16 | class List{
      |       ^~~~
a.cc: In member function 'void List::print()':
a.cc:91:32: error: no match for 'operator!=' (operand types are 'Node*' and 'Node')
   91 |         for(Node* p=head.next;p!=head;p=p->next){
      |                               ~^~~~~~
      |                               |  |
      |                               |  Node
      |                               Node*
In file included from /usr/include/c++/14/iosfwd:42,
                 from /usr/include/c++/14/ios:40,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/postypes.h:197:5: note: candidate: 'template<class _StateT> bool std::operator!=(const fpos<_StateT>&, const fpos<_StateT>&)'
  197 |     operator!=(const fpos<_StateT>& __lhs, const fpos<_StateT>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/postypes.h:197:5: note:   template argument deduction/substitution failed:
a.cc:91:34: note:   mismatched types 'const std::fpos<_StateT>' and 'Node*'
   91 |         for(Node* p=head.next;p!=head;p=p->next){
      |                                  ^~~~
In file included from /usr/include/c++/14/string:43,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44:
/usr/include/c++/14/bits/allocator.h:243:5: note: candidate: 'template<class _T1, class _T2> bool std::operator!=(const allocator<_CharT>&, const allocator<_T2>&)'
  243 |     operator!=(const allocator<_T1>&, const allocator<_T2>&)
      |     ^~~~~~~~
/usr/include/c++/14/bits/allocator.h:243:5: note:   template argument deduction/substitution failed:
a.cc:91:34: note:   mismatched types 'const std::allocator<_CharT>' and 'Node*'
   91 |         for(Node* p=head.next;p!=head;p=p->next){
      |                                  ^~~~
In file included from /usr/include/c++/14/string:48:
/usr/include/c++/14/bits/stl_iterator.h:455:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator!=(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  455 |     operator!=(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:455:5: note:   template argument deduction/substitution failed:
a.cc:91:34: note:   mismatched types 'const std::reverse_iterator<_Iterator>' and 'Node*'
   91 |         for(Node* p=head.next;p!=head;p=p->next){
      |                                  ^~~~
/usr/include/c++/14/bits/stl_iterator.h:500:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator!=(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  500 |     operator!=(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:500:5: note:   template argument deduction/substitution failed:
a.cc:91:34: note:   mismatched types 'const std::reverse_iterator<_Iterator>' and 'Node*'
   91 |         for(Node* p=head.next;p!=head;p=p->next){
      |                                  ^~~~
/usr/include/c++/14/bits/stl_iterator.h:1686:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator!=(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1686 |     operator!=(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1686:5: note:   template argument deduction/substitution failed:
a.cc:91:34: note:   mismatched types 'const std::move_iterator<_IteratorL>' and 'Node*'
   91 |         for(Node* p=head.next;p!=head;p=p->next){
      |                                  ^~~~
/usr/include/c++/14/bits/stl_iterator.h:1753:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator!=(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1753 |     operator!=(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1753:5: note:   template argument deduction/substitution failed:
a.cc:91:34: note:   mismatched types 'const std::move_iterator<_IteratorL>' and 'Node*'
   91 |         for(Node* p=head.next;p!=head;p=p->next){
      |                                  ^~~~
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/string:51:
/usr/include/c++/14/bits/stl_pair.h:1052:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator!=(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1052 |     operator!=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1052:5: note:   template argument deduction/substitution failed:
a.cc:91:34: note:   mismatched types 'const std::pair<_T1, _T2>' and 'Node*'
   91 |         for(Node* p=head.next;p!=head;p=p->next){
      |                                  ^~~~
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54:
/usr/include/c++/14/string_view:651:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator!=(basic_string_view<_CharT, _Traits>, basic_string_view<_CharT, _Traits>)'
  651 |     operator!=(basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:651:5: note:   template argument deduction/substitution failed:
a.cc:91:34: note:   mismatched types 'std::basic_string_view<_CharT, _Traits>' and 'Node*'
   91 |         for(Node* p=head.next;p!=head;p=p->next){
      |                                  ^~~~
/usr/include/c++/14/string_view:658:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator!=(basic_string_view<_CharT, _Traits>, __type_identity_t<basic_string_view<_CharT, _Traits> >)'
  658 |     operator!=(basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:658:5: note:   template argument deduction/substitution failed:
a.cc:91:34: note:   mismatched types 'std::basic_string_view<_CharT, _Traits>' and 'Node*'
   91 |         for(Node* p=head.next;p!=head;p=p->next){
      |                                  ^~~~
/usr/include/c++/14/string_view:666:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator!=(__type_identity_t<basic_string_view<_CharT, _Traits> >, basic_string_view<_CharT, _Traits>)'
  666 |     operator!=(__type_identity_t<basic_string_view<_CharT, _Traits>> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:666:5: note:   template argument deduction/substitution failed:
a.cc:91:34: note:   'Node' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   91 |         for(Node* p=head.next;p!=head;p=p->next){
      |                                  ^~~~
/usr/include/c++/14/bits/basic_string.h:3833:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator!=(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3833 |     operator!=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3833:5: note:   template argument deduction/substitution failed:
a.cc:91:34: note:   mismatched types 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>' and 'Node*'
   91 |         for(Node* p=head.next;p!=head;p=p->next){
      |                                  ^~~~
/usr/include/c++/14/bits/basic_string.h:3847:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator!=(const _CharT*, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3847 |     operator!=(const _CharT* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3847:5: note:   template argument deduction/substitution failed:
a.cc:91:34: note:   'Node' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   91 |         for(Node* p=head.next;p!=head;p=p->next){
      |                                  ^~~~
/usr/include/c++/14/bits/basic_string.h:3860:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator!=(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*)'
 3860 |     operator!=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3860:5: note:   template argument deduction/substitution failed:
a.cc:91:34: note:   mismatched types 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>' and 'Node*'
   91 |         for(Node* p=head.next;p!=head;p=p->next){
      |                                  ^~~~
In file included from /usr/include/c++/14/bits/memory_resource.h:47,
                 from /usr/include/c++/14/string:68:
/usr/include/c++/14/tuple:2613:5: note: candidate: 'template<class ... _TElements, class ... _UElements> constexpr bool std::operator!=(const tuple<_UTypes ...>&, const tuple<_Elements ...>&)'
 2613 |     operator!=(const tuple<_TElements...>& __t,
      |     ^~~~~~~~
/usr/include/c++/14/tuple:2613:5: note:   template argument deduction/substitution failed:
a.cc:91:34: note:   mismatched types 'const std::tuple<_UTypes ...>' and 'Node*'
   91 |         for(Node* p=head.next;p!=head;p=p->next){
      |                                  ^~~~
In file included from /usr/include/c++/14/bits/locale_facets.h:48,
                 from /usr/include/c++/14/bits/basic_ios.h:37,
                 from /usr/inclu