C :: Segmentation Fault In Header File?

I have written a small program for a class to convert decimal to binary and the program itself works, however, I am storing the binary bits in a stack that is in a header file (which I have used successfully before). It appears to push the bits to the stack just fine, however, when I use the printStack function I get a segmentation fault.

Here is the stack.h header file:

Code:
#include <stdlib.h>
#include <stdio.h>
struct stackNode {
int data;
struct stackNode *nextPtr;

[Code].....

And here is the main program that does the conversion:

Code:
#include <stdio.h>
#include "stack.h"
int binary (int x);
int main() {
int choice = 0;
printf("

[Code].....

One other thing of note, whenever I try to modify the printStack function, that function then seems to not work at all.