Pushing to a stack containing ONLY unique values in C

Question

I've implemented a stack with pointers, that works like it's suppose too. Now, I need it push to the stack, without it pushing a duplicate. For example, if I push '2' into the stack, pushing another '2' will still result with only one '2' in the stack because it already exists.

Below is how I went about trying to create the new push function. I know that I'm suppose to traverse the stack and check it for the element I'm adding, but I guess I'm doing that wrong? Can anyone help me out?

    typedef struct Node {
        void *content;
        struct Node *next;
    } Node;

    typedef struct Stack {
        Node *head;
        int count; 
    } Stack;

    void push(Stack *stack, void *newElem) {
        Node *newNode = (Node*) malloc(sizeof(Node));
        if (stack->count > 0) {
             int i;
             for (i = 0, newNode = stack->head; i < stack->count; i++, newNode =
                 newNode->next) {
                   if (newNode->content == newElem) return;
             }
        } else {
            newNode->next = stack->head;
            newNode->content = newElem;
            stack->head = newNode;
            stack->count++;
        }
    }

Answer 1

if (newNode->content == newElem)

You are comparing two pointers. I guess you want to check whether their contents are equal:

#include <string.h>

if (memcmp(newNode->content, newElem, size) == 0)

The value size may be indicated by the caller. In your case, it should be sizeof(int).

Moreover, once you have traversed the stack, you don't add the element to your data structure.