c++ - SIGSEGV error with BFS Algorithm -

i have bfs algorithm error. have tried debug gdb don't understand why this.

can tell me why sigsegv error code below. depend on compiler use how pointers addressed? there invalid pointer error in code

#include<iostream> #include<stdlib.h>  #define true 1 #define false 0  using namespace std;  const int max = 8;  struct node {   int data;   node *next; };  class graph {   private:      int visited[max];     int q[8];     int front, rear;  public:      graph();     void bfs(int v, node **p);     node *getnode_write(int val);     static void addqueue(int *a, int vertex, int *f, int *r);     static int deletequeue(int *q, int *f, int *r);     static int isempty(int *f);     void del(node *n); };  // initialize data memeber graph::graph() {    for(int = 0; < max; i++)         visited[i] = false;     front = rear = -1; }  // function implements breadth first search (bfs) algorithm void graph::bfs(int v, node **p) {     node *u;      visited[v-1] = true;      cout<<v<<"\t";     addqueue(q, v, &front, &rear);     while(isempty(&front) == false)    {        v = deletequeue(q, &front, &rear);        u = *(p+v-1);         while(u != null)        {           if(visited[u->data-1] == false)           {             addqueue(q, u->data, &front, & rear);             visited[u->data-1] == true;             cout<<u->data<<"\t";           }            u = u->next;        }                   }   }   // creates node  node *graph::getnode_write(int val)  {      node *newnode = new node;      newnode->data = val;      return newnode;  }   //adds node queue  void graph::addqueue(int *a, int vertex, int *f, int *r)  {     if(*r == max -1)     {        cout<<"\nqueue overflow.";        exit(0);     }      (*r)++;      a[*r] = vertex;      if(*f == -1)        *r = 0;    }     // deletes node queue    int graph::deletequeue(int *a, int *f, int *r)    {        int data;         if(*f == -1)        {          cout<<"\nqueue underflow";          exit(0);        }         data = a[*f];         if(*f == *r)           *f = *r = -1;        else          (*f)++;        return data;           }      // checks if queque empty   int graph::isempty(int *f)   {      if(*f == -1)         return true;     return false;   }     // deallocate memory   void graph::del(node *n)    {        node *temp;        while(n != null)       {            temp = n->next;            delete n;            n = temp;       }    }    int main()   {       node *arr[max];       node *v1,*v2,*v3,*v4;        graph g;        v1 = g.getnode_write(2);         arr[0] = v1;         v1->next = v2 = g.getnode_write(3);       v2->next = null;        v1 = g.getnode_write(1);       arr[1] = v1;       v1->next = v2 = g.getnode_write(4);       v2->next = v3 = g.getnode_write(5);       v3->next = null;          cout<<endl;        g.bfs(1,arr);        for(int = 0; i<max; i++)           g.del(arr[i]);           } 

there uninitialized array arr in stack frame of main. arr[0] , arr[1] become initialized. @ end of main iterated on whole array , delete called in graph::del(node *n) on garbage value.