Working with linked lists. Why my insert function is not working?

I am trying to insert numbers which are a result of deduction of two neighbors in already made up list.

        #include<iostream>

        using namespace std;

        struct Element{
            int x;
            Element* next;
        };

        Element* createList(){
            int i,n;
            Element *head=NULL,*p=NULL;
            cout<<"How many elements: ";
            cin>>n;
            for(i=0;i<n;i++){
                if(i==0) {
                    head=new Element();
                    p=head;
                }
                else{
                    p->next=new Element();
                    p=p->next;
                }
                cout<<"Value: ";
                cin>>p->x;
            }
            p->next=NULL;
            return head;
        }

        void printList(Element* head){
            Element* p=head;
            cout<<"List values: "<<endl;
            while(p!=NULL){
                cout<<p->x<<"   ";
                p=p->next;
            }
            cout<<endl;
        }

        Element* createElement(int x){
            Element* element=new Element();
            element->x=x;
            element->next=NULL;
            return element;
        }


        Element* insert(Element* head){
            Element *p=head,*temp=NULL;
            while(p->next!=NULL){
                temp=createElement(p->next->x - p->x);
                temp->next=p->next;
                p->next=temp;
                p=p->next;
            }
            return head;
        }


        int main(){
            Element* head=NULL;
            head=createList();
            printList(head);
            head=insert(head);
            printList(head);
            return 0;
        }

I expected that my updated list will contain these numbers which should be placed between every two numbers in the original list but when my program encounters the insert function it is just running and never finishes. Example: Original list: 1 5 8 12 30 Updated list: 1 4 5 3 8 4 12 18 30