devc++編譯出錯

#include<iostream>
using namespace std;
class Solution{
	public:
		ListNode* getKthFromEnd(ListNode* head, int k){
			int count = 0;
			int length = 1;
			ListNode via;
			via = head;
			while(via->next != null){
				via = via->next;
				length++;
			}
			while(count != length -
 
 k){
				head = head->next;
				count++;
			}
			return head;
		}
}; 

struct ListNode {
     int val;
     ListNode *next;
     ListNode(int x) : val(x), next(NULL) {}
 };

導師讓學c++，求助各位前輩幫忙指正錯誤！