Language: C++

#include <iostream>
#include <iomanip>
#include <vector>
#include <string>
#include <stack>
#include <set>
#include <cmath>
#include <algorithm>
#include <cstdio>
using namespace std;

struct Node {
	long long int value;
	Node* prev;
	Node* next;
};

Node* root = new Node;

void insert_key(long long int x){
	if(root->next==NULL){
		root->value=x;
		Node* tmp = new Node;
		root->next=tmp;
		tmp->prev=root;
		tmp->next=NULL;
		tmp->value=0;
	} else {
		Node* tmp = new Node;
		tmp->prev=NULL;
		tmp->next=root;
		tmp->value=x;
		root->prev=tmp;
		root=tmp;
	}
}
void delete_key(long long int x){
	for(Node* tmp=root ; tmp->next!=NULL ; tmp=tmp->next){
		if(tmp->value==x) {
			Node* tmp2=tmp->prev;
			tmp2->next=tmp->next;
			Node* tmp3=tmp->next;
			tmp3->prev=tmp2;
			delete tmp;
			break;
		}
	}
		
}
void delete_first(){
	Node* tmp=root;
	root=root->next;
	root->prev=NULL;
	delete tmp;
}

void delete_last(){
	Node *tmp=root;
	while(tmp->next!=NULL) tmp=tmp->next;
	Node *tmp2=tmp->prev;
	tmp2->next=NULL;
	delete tmp;
}



int main(){
	int n , i;
	cin >> n;
	vector<string> v(n);
	long long int* x = new long long int [n]; 
	root->prev=NULL; root->next=NULL; root->value=0;
	for(i=0 ; i<n ;++i){
		cin >> v[i];
		if(v[i]=="insert"){
			cin >> x[i];
			insert_key(x[i]);
		} else if (v[i]=="delete"){
			cin >> x[i];
			delete_key(x[i]);
		} else if (v[i]=="deleteFirst"){
			delete_first();
		} else if (v[i]=="deleteLast"){
			delete_last();
		}
	}
	for(Node* tmp=root ; tmp->next!=NULL ; tmp=tmp->next){
		cout << tmp->value << " ";
		delete tmp;
	}
????????????cout << endl;
	return 0; 
}

Compiler output:
a.cc: In function 'int main()':
a.cc:91:1: error: expected primary-expression before '?' token
   91 | ????????????cout << endl;
      | ^
a.cc:91:2: error: expected primary-expression before '?' token
   91 | ????????????cout << endl;
      |  ^
a.cc:91:3: error: expected primary-expression before '?' token
   91 | ????????????cout << endl;
      |   ^
a.cc:91:4: error: expected primary-expression before '?' token
   91 | ????????????cout << endl;
      |    ^
a.cc:91:5: error: expected primary-expression before '?' token
   91 | ????????????cout << endl;
      |     ^
a.cc:91:6: error: expected primary-expression before '?' token
   91 | ????????????cout << endl;
      |      ^
a.cc:91:7: error: expected primary-expression before '?' token
   91 | ????????????cout << endl;
      |       ^
a.cc:91:8: error: expected primary-expression before '?' token
   91 | ????????????cout << endl;
      |        ^
a.cc:91:9: error: expected primary-expression before '?' token
   91 | ????????????cout << endl;
      |         ^
a.cc:91:10: error: expected primary-expression before '?' token
   91 | ????????????cout << endl;
      |          ^
a.cc:91:11: error: expected primary-expression before '?' token
   91 | ????????????cout << endl;
      |           ^
a.cc:91:12: error: expected primary-expression before '?' token
   91 | ????????????cout << endl;
      |            ^
a.cc:91:25: error: expected ':' before ';' token
   91 | ????????????cout << endl;
      |                         ^
      |                         :
a.cc:91:25: error: expected primary-expression before ';' token
a.cc:91:25: error: expected ':' before ';' token
   91 | ????????????cout << endl;
      |                         ^
      |                         :
a.cc:91:25: error: expected primary-expression before ';' token
a.cc:91:25: error: expected ':' before ';' token
   91 | ????????????cout << endl;
      |                         ^
      |                         :
a.cc:91:25: error: expected primary-expression before ';' token
a.cc:91:25: error: expected ':' before ';' token
   91 | ????????????cout << endl;
      |                         ^
      |                         :
a.cc:91:25: error: expected primary-expression before ';' token
a.cc:91:25: error: expected ':' before ';' token
   91 | ????????????cout << endl;
      |                         ^
      |                         :
a.cc:91:25: error: expected primary-expression before ';' token
a.cc:91:25: error: expected ':' before ';' token
   91 | ????????????cout << endl;
      |                         ^
      |                         :
a.cc:91:25: error: expected primary-expression before ';' token
a.cc:91:25: error: expected ':' before ';' token
   91 | ????????????cout << endl;
      |                         ^
      |                         :
a.cc:91:25: error: expected primary-expression before ';' token
a.cc:91:25: error: expected ':' before ';' token
   91 | ????????????cout << endl;
      |                         ^
      |                         :
a.cc:91:25: error: expected primary-expression before ';' token
a.cc:91:25: error: expected ':' before ';' token
   91 | ????????????cout << endl;
      |                         ^
      |                         :
a.cc:91:25: error: expected primary-expression before ';' token
a.cc:91:25: error: expected ':' before ';' token
   91 | ????????????cout << endl;
      |                         ^
      |                         :
a.cc:91:25: error: expected primary-expression before ';' token
a.cc:91:25: error: expected ':' before ';' token
   91 | ????????????cout << endl;
      |                         ^
      |                         :
a.cc:91:25: error: expected primary-expression before ';' token
a.cc:91:25: error: expected ':' before ';' token
   91 | ????????????cout << endl;
      |                         ^
      |                         :
a.cc:91:25: error: expected primary-expression before ';' token