Функция размера связанного списка ?

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here i have problem i think in the size function i want to have the size of the whole linked list before and after deletion basically, the size function says error that "size must return value" and return value does not match return type !! cheers for help !! Thanks

В основном я выделил недостаток !!

Что я уже пробовал:

//SLL Basic insert , delete and search functions

#include<iostream>
using namespace std;

/* defines the structure of a single linked list node*/
typedef struct list_node {
    int data;
    struct list_node *next; // pointer to next node in the list 
}node;

/* create new node */
node *getNewNode(int data) {
    node *new_node = new node;
    new_node->data = data;
    new_node->next = NULL;
    return new_node;
}

/* get size of list */
node* size(node *head)
{
    int len = 0;
    while (head != NULL)
    {
        len++;
        head = head->next;

    }
    return len;
}

/* displays the list elements */
void displayList(node *head) {
    cout << "Displaying List : ";
    while (head != NULL) {
        cout << head->data << " -> ";
        head = head->next;
    }
    cout << "NULL " << endl;
}

/* Search the node with element as data
Return the pointer to the node if found else return NULL */
node *searchNode(node *head, int data) {
    node *ptr = NULL;
    while (head) {
        if (head->data == data) {
            ptr = head;
            break;
        }
        head = head->next;
    }
    return ptr;
}

/* insert a node at the beginning of the list */
node *insertNodeBeg(node *head, int data) {
    node *ptr = getNewNode(data);
    if (head == NULL) { // if list is empty
        head = ptr;
    }
    else {
        ptr->next = head;
        head = ptr;
    }
    return head;
}

/* insert a node at the end of the list */
node *insertNodeEnd(node *head, int data) {
    node *ptr = getNewNode(data);
    if (head == NULL) { //if list is empty
        head = ptr;
    }
    else {
        node *temp = head;
        while (temp->next != NULL) { // move to the last node
            temp = temp->next;
        }
        temp->next = ptr; // insert node at the end
    }
    return head;
}

/* insert a node at the after a particular node in the list */
node *insertNodeAfter(node *head, int element, int data) {
    // search the element after which node is to be inserted
    node *temp = searchNode(head, element);
    if (temp == NULL) { // element not found
        cout << "Element not found ... " << endl;
    }
    else {
        node *ptr = getNewNode(data);
        if (temp->next == NULL) { // node has to inserted after the last node
            temp->next = ptr;
        }
        else {  // insert the node after the first or an intermediate node
            ptr->next = temp->next;
            temp->next = ptr;
        }
    }
    return head;
}

/* delete a particular node from the list */
node *deleteNode(node *head, int element) {
    node *temp = searchNode(head, element); // search the node to be deleted
    if (temp == NULL) { // element not found
        cout << "Node to be deleted not found ... " << endl;
    }
    else {
        if (temp == head) { // first node is to be deleted
            head = head->next;
            delete temp;
        }
        else { // node to deleted is an intermediate or last node
            node *ptr = head;
            while (ptr->next != temp) {
                ptr = ptr->next;
            }
            ptr->next = temp->next;
            delete temp;
        }
    }
    return head;
}

int main() 
{
    node *head = NULL;
    head = insertNodeBeg(head, 7);       // 7
    head = insertNodeBeg(head, 9);       // 9 -> 7
    head = insertNodeEnd(head, 11);      // 9 -> 7 -> 11
    head = insertNodeAfter(head, 9, 4);  // 9 -> 4 -> 7 -> 11
    head = insertNodeAfter(head, 7, 3);  // 9 -> 4 -> 7 -> 3 -> 11
    head = insertNodeAfter(head, 11, 6); // 9 -> 4 -> 7 -> 3 -> 11 -> 6
    head = size(head);// HERE i want to give size of LIST i,e 6 in this case !! 
    displayList(head);
    head = deleteNode(head, 7);          // 9 -> 4 -> 3 -> 11 -> 6
    head = deleteNode(head, 6);          // 9 -> 4 -> 3 -> 11
    head = deleteNode(head, 9);          // 4 -> 3 -> 11
    head = deleteNode(head, 3);         // 4 -> 11
    displayList(head);
    return 0;
}

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