Unhandled exception thrown: read access violation. top was nullptr.

#include <stdio.h>
#include <stdlib.h>

Typedef struct list {// The connection with the address list structure and key. that declaration, named node
    int key;
    struct list* next;
} node;

node* top, * bottom;

int init_stack() { //initialization
    top = (node*)malloc(sizeof(node));
    bottom = (node*)malloc(sizeof(node));
    top->next = bottom;
    bottom->next = bottom;
    return 0;
}

Int print the output () {//.
    puts("");
    node* p;
    p = top->next;
    while (p != bottom) {
        printf("%d ", p->key);
        p = p->next;
    }
    puts("");
    return 0;
}

int push(int n) { //push
    node* p;
    if ((p = (node*)malloc(sizeof(node))) == NULL) {
        printf ("Memory Exceeded\n");
        return -1;
    }
    printf("push %d ", n);
    p->key = n;
    p->next = top->next; //p becomes the top of the stack
    top->next = p; //p followed by push
    print();
    return n;
}
int pop() {//pop
    node* p; // temporary node to delete
    intn; // For integer value return deleted after deletion
    if (top->next == bottom) { //Check if the stack is empty
        printf ("Nothing in Stack\n");
        return -1;
    }
    p = top->next; //top_next Save to p for node deletion
    n = p->key; //Save the key value of the p you want to delete
    printf("pop %d ", n);
    top->next = p->next; //head->next node points to the next node on the node you want to delete
    free(p); //p Delete
    print();
    return n;
}
int clear() { // Empty the stack
    node* p, * q;
    p = top->next; //Save the first node in p
    while (p != bottom) {
        q = p; // Save in q to delete node
        p = p->next; //p crosses to the next node
        free(q); //Delete Saved Node
    } //If you don't delete a saved node, it's a waste of memory
    top->next = bottom;
    printf ("stack empty\n");
    return 0;
}
int main() {
    init_stack();
    push(1);
    push(2);
    pop();
    push(3);
    clear();
    pop();
    return 0;
}