Problem p02265 (C++) — buggy submission, verdict: Runtime Error

#include <cstdio>
#include <cstdlib>
#include <cstring>

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

Node *nil;

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

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

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

void deleteFirst() { deleteNode(nil->next); }

void deleteLast() { deleteNode(nil->prev); }

void deleteKey(int key) { deleteNode(listSearch(key)); }

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;
  char com[20];
  scanf("%d", &n);
  init();
  for (i = 0; i < n; i++) {
    scanf("%s%d", com, &key);
    if (com[0] == 'i') {
      insert(key);
    } else if (com[0] == 'd') {
      if (strlen(com) > 6) {
        if (com[6] == 'F') {
          deleteFirst();
        } else if (com[6] == 'L') {
          deleteLast();
        }
      } else {
        deleteKey(key);
      }
    }
  }
  printList();
}

Error: 0

Fixed submission:

#include <cstdio>
#include <cstdlib>
#include <cstring>
typedef struct Node {
  int key;
  struct Node *prev;
  struct Node *next;
} Node;

Node *head;

void initNode() {
  head = (Node *)malloc(sizeof(Node));
  head->prev = NULL;
  head->next = NULL;
}

void insertFirst(int key) {
  Node *x = (Node *)malloc(sizeof(Node));
  x->key = key;
  if (head->next == NULL) {
    head->next = x;
    x->prev = head;
    x->next = NULL;
  } else {
    x->next = head->next;
    x->next->prev = x;
    head->next = x;
    x->prev = head;
  }
}

inline Node *listSearch(int key) {
  Node *current = head->next;
  while (current != NULL && current->key != key) {
    current = current->next;
  }
  return current;
}

inline void deleteFirst() {
  Node *t = head->next;
  head->next = t->next;
  t->next->prev = head;
}

inline void deleteLast() {
  Node *t = head->next;
  while (t->next != NULL) {
    t = t->next;
  }
  t->prev->next = NULL;
}

void deleteNode(int key) {
  Node *x = listSearch(key);
  if (x == NULL) {
    return;
  } else if (x->next == NULL) {
    x->prev->next = NULL;
    free(x);
    x = NULL;
    return;
  }
  x->prev->next = x->next;
  x->next->prev = x->prev;
}

int main() {
  initNode();
  int n;
  scanf("%d", &n);
  char com[20];
  int x;
  for (int i = 0; i < n; i++) {
    scanf("%s", com);
    if (com[6] == '\\0') {
      scanf("%d", &x);
      if (com[0] == 'i') {
        insertFirst(x);
      } else if (com[0] == 'd') {
        deleteNode(x);
      }
    } else {
      if (com[6] == 'F') {
        deleteFirst();
      } else if (com[6] == 'L') {
        deleteLast();
      }
    }
  }
  Node *temp = head->next;
  int isf = 0;
  while (temp != NULL) {
    if (isf++ > 0)
      printf(" ");
    printf("%d", temp->key);
    temp = temp->next;
  }
  printf("\\n");
  return 0;
}