Problem using two stacks with following code

Im getting crashes if I initialize more than one stack using this code.

Code:

---


struct stackNode{
       
        int data;
        struct stackNode *nextptr;
};

int pop(struct stackNode **topptr)
        {
               
                struct stackNode *tmp;
               
                if( *topptr != NULL)
                {
                        tmp = *topptr;
                        *topptr = (struct stackNode *) tmp->nextptr;
                        int temp2;
                        temp2 = tmp->data;
                        free(tmp);
                        return temp2;
                }
                else{
                        printf("Pop function error.");
                        exit(0);
               
                }
               
       
        }
       
        void push(struct stackNode **topptr, int info)
        {
               
                struct stackNode *temp;
               
                temp = (struct stackNode *)malloc(sizeof(struct stackNode));
               
                        temp->data = info;
                        temp->nextptr = *topptr;
                        *topptr = temp;
                       
        }

---

I am initializing in Main using

Code:

---

struct stackNode **xstack;
struct stackNode **ystack;

---

if I only initialize one I don't crash until I try to use the second initialized stack.

Example:

Code:

---

struct stackNode **xstack;
push(xstack, 5);
push(xstack, 5);


printf("%d %d", pop(xstack), pop(xstack));

---

works fine.

If I try

Code:

---

struct stackNode **xstack;
struct stackNode **ystack

push(xstack, 5);
push(ystack, 5);

printf("%d %d", pop(xstack), pop(ystack));

---

I will crash.

Code:

---

struct stackNode **xstack;
push(xstack, 5);
push(xstack, 5);


printf("%d %d", pop(xstack), pop(xstack));

---

u have just defined a stacknode pointer,that pointer needs to point somewhere, so use something like this:

Code:

---

struct stackNode xstack;
struct stackNode* xstack_p;
xstack_p = &xstack;


push(&xstack_p, 5);
push(&xstack_p, 5);


printf("%d %d", pop(&xstack_p), pop(&xstack_p));
}

---

use this.




for two stacks

Code:

---

struct stackNode xstack;
struct stackNode* xstack_p;
xstack_p = &xstack;

struct stackNode ystack;
struct stackNode* ystack_p;
ystack_p = &ystack;

---

thanks a bunch