rename Data Structure -> data_structure (#644)

data_structure/Queue Using Linked List.cpp

@@ -0,0 +1,89 @@
+#include <iostream>
+using namespace std;
+
+struct node
+{
+    int val;
+    node *next;
+};
+
+node *front, *rear;
+
+void Enque(int x)
+{
+    if (rear == NULL)
+    {
+        node *n = new node;
+        n->val = x;
+        n->next = NULL;
+        rear = n;
+        front = n;
+    }
+
+    else
+    {
+
+        node *n = new node;
+        n->val = x;
+        n->next = NULL;
+        rear->next = n;
+        rear = n;
+    }
+}
+
+void Deque()
+{
+    if (rear == NULL && front == NULL)
+    {
+        cout << "\nUnderflow";
+    }
+    else
+    {
+        node *t = front;
+        cout << "\n"
+             << t->val << " deleted";
+        front = front->next;
+        delete t;
+        if (front == NULL)
+            rear = NULL;
+    }
+}
+
+void show()
+{
+    node *t = front;
+    while (t != NULL)
+    {
+        cout << t->val << "\t";
+        t = t->next;
+    }
+}
+
+int main()
+{
+    int ch, x;
+    do
+    {
+        cout << "\n1. Enque";
+        cout << "\n2. Deque";
+        cout << "\n3. Print";
+        cout << "\nEnter Your Choice : ";
+        cin >> ch;
+        if (ch == 1)
+        {
+            cout << "\nInsert : ";
+            cin >> x;
+            Enque(x);
+        }
+        else if (ch == 2)
+        {
+            Deque();
+        }
+        else if (ch == 3)
+        {
+            show();
+        }
+    } while (ch != 0);
+
+    return 0;
+}