feat: Moving queue file to it's directory and creating include file for it (#874)

* Putting queue in correct dir and creating include file for it

* Update data_structures/queue/include.h

missing one function, added

Co-authored-by: David Leal <halfpacho@gmail.com>

Co-authored-by: David Leal <halfpacho@gmail.com>

data_structures/queue/include.h

@@ -0,0 +1,28 @@
+//////////////////////////////////////////////////////////////////////////////////////
+/// INCLUDES
+
+#include <stdio.h>
+#include <stdlib.h>
+////////////////////////////////////////////////////////////////////////////////
+// DATA STRUCTURES
+/**
+ * Defining the structure of the node which contains 'data' (type : integer),
+ * two pointers 'next' and 'pre' (type : struct node).
+ */
+
+struct node
+{
+    int data;
+    struct node *next;
+    struct node *pre;
+} * head, *tail, *tmp;
+
+////////////////////////////////////////////////////////////////////////////////
+// FORWARD DECLARATIONS
+
+void create();
+void enque(int x);
+int deque();
+int peek();
+int size();
+int isEmpty();

data_structures/queue/queue.c

@@ -0,0 +1,73 @@
+////////////////////////////////////////////////////////////////////////////////
+// INCLUDES
+#include "include.h";
+
+////////////////////////////////////////////////////////////////////////////////
+// GLOBAL VARIABLES
+int count;
+
+////////////////////////////////////////////////////////////////////////////////
+// MAIN ENTRY POINT
+
+int main(int argc, char const *argv[])
+{
+    create();
+    enque(5);
+
+    return 0;
+}
+
+void create()
+{
+    head = NULL;
+    tail = NULL;
+}
+
+/**
+ * Puts an item into the Queue.
+ */
+void enque(int x)
+{
+    if (head == NULL)
+    {
+        head = (struct node *)malloc(sizeof(struct node));
+        head->data = x;
+        head->pre = NULL;
+        tail = head;
+    }
+    else
+    {
+        tmp = (struct node *)malloc(sizeof(struct node));
+        tmp->data = x;
+        tmp->next = tail;
+        tail = tmp;
+    }
+}
+
+/**
+ * Takes the next item from the Queue.
+ */
+int deque()
+{
+    int returnData = 0;
+    if (head == NULL)
+    {
+        printf("ERROR: Deque from empty queue.\n");
+        exit(1);
+    }
+    else
+    {
+        returnData = head->data;
+        if (head->pre == NULL)
+            head = NULL;
+        else
+            head = head->pre;
+        head->next = NULL;
+    }
+    return returnData;
+}
+
+/**
+ * Returns the size of the Queue.
+ */
+int size() { return count; }