Linked list variation - c

Question

I am in a bit of a pickle. I have a variation of a linked list where not only do the nodes contain a value, but also each node will have a flag declaring whether it is a valid node or not (1 is valid; 0 is invalid). I have some functions that I am having difficulty with. I have deleteLast which deletes the last valid node, or in other words, clears the valid flag to 0. Bear in mind the last valid node might not be the last node; I was hoping countNodes would of use here. deleteValue 'deletes' first valid node with specified value. restoreValue restores the first 'deleted' node with specified value. lastly, compact makes a new list of valid nodes only in reverse order of the old list. deleteLast is the function I'm having most difficulty with. Any feedback on that function or any of the other functions will be of great help. Here's some code:
#include <stdio.h>
#include <stddef.h>
#include <stdlib.h>
struct Node{
struct Node *link;
int value;
int valid;
}
int countNodes (Node *ptrToFirst){
int count=0;
if(ptrToFirst==NULL){
return 0;
}
else{
while(ptrToFirst!=NULL){
if(ptrToFirst->valid==1)
count++;
ptrToFirst=ptrToFirst->link;
}
}
int deleteLast(Node *ptrToFirst){
Node p;
if(countNodes||ptrToFirst!=NULL){
while(ptrToFirst!=NULL){
ptrToFirst->link;
if(ptrToFirst->valid==1)
if(ptrToFirst->link==NULL){
}
}
}
else return 0;
}
int deleteValue(Node *ptrToFirst, int val){
if(ptrToFirst==NULL){
return 0;
}
while(ptrToFirst!=NULL){
if(ptrToFirst->value==val&&ptrToFirst->valid==1){
ptrToFirst->valid=0;
return 0;
}
else
ptrToFirst=ptrToFirst->link;
}
}
int restoreValue(Node *start, int val){
if(start==NULL){
return 0;
}
while(start!=NULL){
if(start->value==val&&start->valid==0)
start->valid=1;
return 1;
else
start=start->link;
}
}
int compact(Node *old, **ptrToNewHeadPtr){
Node temp;
if(old!=NULL){
while(old!=NULL){
if(old->valid==1)
temp=old;
*ptrToNewHeadPtr=temp;
old=old->link;
}
return 1;
}
else return 0;
}