LeeCode-Remove Linked List Elements

Remove all elements from a linked list of integers that have value val.

Example
Given: 1 --> 2 --> 6 --> 3 --> 4 --> 5 --> 6, val = 6
Return: 1 --> 2 --> 3 --> 4 --> 5

 /**
  * Definition for singly-linked list.
  * struct ListNode {
  *     int val;
  *     struct ListNode *next;
  * };
  */
 struct ListNode* removeElements(struct ListNode* head, int val)
 {
         if(head==NULL)
         return NULL;

     if(head->next==NULL&&head->val==val)
     {
         return NULL;
     }

     if(head->next==NULL&&head->val!=val)
     {
         return head;
     }

     struct ListNode *p=head;

     while(p->val==val&&p->next!=NULL)
     {
         p=p->next;
     }

     if(p->val==val)
     {
         return NULL;
     }

     head=p;

     if(p->next==NULL)
     {
         return head;
     }

     while(p->next->next!=NULL)
     {
         if(p->next->val==val)
         {
             p->next=p->next->next;
             continue;
         }
         p=p->next;
     }

     if(p->next->val==val)
     {
         p->next=NULL;
     }

     return head;
 }