read violation resolved (#1496)

data_structures/circular_queue_using_linked_list.cpp

@@ -2,34 +2,27 @@
 
 struct node {
     int data;
-    struct node *next;
+    struct node* next;
 };
 class Queue {
-    node *front;
-    node *rear;
+    node* front=nullptr;
+    node* rear=nullptr;
 
- public:
-    Queue() {
-        front = NULL;
-        rear = NULL;
-    }
+public:
+    Queue() = default; 
     void createNode(int val) {
-        node *ptr;
-        node *nn;
-        nn = new node;
-        ptr = front;
+        auto* nn = new node;
         nn->data = val;
-        nn->next = NULL;
+        nn->next = nullptr;
         front = nn;
         rear = nn;
     }
     void enqueue(int val) {
-        if (front == NULL || rear == NULL) {
+        if (front == nullptr || rear == nullptr) {
             createNode(val);
-        } else {
-            node *ptr;
-            node *nn;
-            ptr = front;
+        }
+        else {
+            node* nn;
             nn = new node;
             nn->data = val;
             rear->next = nn;
@@ -38,20 +31,24 @@ class Queue {
         }
     }
     void dequeue() {
-        node *n;
+        node* n;
         n = front;
+        if (n) {
             front = front->next;
-        delete (n);
+            delete n;
+        }
     }
     void traverse() {
-        node *ptr;
+        node* ptr;
         ptr = front;
+        if (ptr) {
             do {
                 std::cout << ptr->data << " ";
                 ptr = ptr->next;
             } while (ptr != rear->next);
             std::cout << front->data << std::endl;
         }
+    }
 };
 int main(void) {
     Queue q;