Create Queue Usung doubly Linked list with mid pointer maintainance

Data Structures/Queue Usung doubly Linked list with mid pointer maintainance

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+#include<bits/stdc++.h>
+using namespace std;
+
+struct doublyqueue {
+	int d;
+	doublyqueue* next=NULL;
+	doublyqueue* prev=NULL;
+};
+doublyqueue *front=NULL;
+doublyqueue *rear=NULL;
+doublyqueue *mid=NULL;
+//  f->null r->null mid =null
+// f->1<-r mid=1 i.e when changed from even to odd by push mid updated
+// f->1>2><r mid =1 odd to ev no ch
+//f->1>2>3<r mid=2 i.e mid=mid->next when changed to odd and n!=1
+//del 1 i.e deque => mid= 2 i.e mid= mid->prev i.e
+
+
+// now check for delete mid ex only  1 then mid=null
+//if 1 2 mid=1 and delmid=> mid=m->next;
+// if 1 2 3 mid= 2 del mid => mid=m->prev;
+// 1 2 3 4 m=2 del 2 => 1 3 4 mid = 3 i.e m->next;
+// i.e size reduced and if new size is odd => m=m->next
+int size=0;
+void push(int data)
+{
+	// push in a queue => insertion at rear
+	doublyqueue *temp= new doublyqueue();
+	temp->d=data;
+	size++;
+
+	// base case if queue is empty
+	if(front==rear && !front)// front=r=NULL
+	{
+		front=temp;
+		rear=temp;
+		mid=temp;
+	}
+	else 
+	{
+		// one element
+		rear->next=temp;
+		temp->prev=rear;
+		rear=temp;
+		if(size%2!=0)// changed from even to odd
+		{
+			mid=mid->next;
+		}
+
+	}
+}
+void  pop()
+{
+	// delete at front
+	int d;
+
+	if(front==rear && !front) // if empty
+	{
+		mid=NULL;
+
+		return;
+		//return -1;
+	}
+	else if( front == rear)
+	{ size--; 
+	d= front->d;
+		front=NULL;
+		rear=front;
+		mid=front;
+	}
+	else
+	{ size--;
+		 d= front->d;
+		front=front->next;
+		front->prev=NULL;
+		if(size%2==0)
+		{
+			mid=mid->prev;
+		}
+	}
+	return;
+	//return d;
+}
+void displayfromfront(doublyqueue *f)
+{
+	while(f!=NULL)
+	{
+	cout<<f->d<<" ";
+	f=f->next;
+	}	
+}
+void printmiddata()
+{
+	if(mid!=NULL)
+	cout<< mid->d<<endl;
+	else
+	cout<< -1<<endl;
+}
+void  printtopdata()
+{
+	int i= front!=NULL ? front->d : -1;
+	cout<<i<<endl;
+}
+void deletemid()
+{
+	size--;
+	if(front==rear && !front)
+	{
+		return ;
+	}
+	else if(front==rear)
+	{
+		front=NULL;
+		rear=NULL;
+
+	}
+	else
+	{
+		doublyqueue* p =mid->prev;
+		doublyqueue* f =mid->next; 
+		p->next=p->next->next;
+		f->prev=p;
+		mid->prev=NULL;
+		mid->next=NULL;
+		if(size%2==0)
+		{
+			mid=p;
+		}
+		else
+		{
+			mid= f;
+		}
+	}
+}
+
+int main(){
+
+    int n; // elements to push
+    cin>>n;
+    while(n--){
+        int d;
+        cin>>d;
+         push(d);
+    }
+    int t; // quries
+    cin>>t;
+    while(t--){
+
+        cin>>n;
+        if(n==1){
+            int x;
+            cin>>x;
+            push(x);
+        }
+        else if(n==2){
+          pop();
+        }
+        else if(n==3){
+
+			deletemid();
+        }
+        else if(n==4){
+             printtopdata(); 
+        }
+        else if(n==5){
+        	printmiddata();
+        }
+        else if(n==6)
+        {
+        	displayfromfront(front);
+		}
+    }
+}