Why my code for deleting a node in BST instead of deletion is assigning a new value like 0 or random value to node to be deleted?

Question

Node* search(Node* &root, int data) {
    if (root == NULL) {
        cout << "key not found\n";
        return NULL;
    }
    if (root -> key == data)
        return root;
    else if(root-> key > data)
        return search(root -> left, data);
    else
        return search(root -> right,data);
}

Node* findMinVal(Node* &root){
    Node* current = root;
    while (current -> left != NULL)
        current = current -> left;
    return current;
}

void deleteNode(Node* &root, int key) {
    if (root == NULL)
        return;
    Node* node = search(root, key);
    if (node -> left == NULL) {
        Node* temp = node;
        node = node -> right;
        free(temp);
    }
    else if (node -> right == NULL) { 
        Node* temp;
        node = node -> left;
        free(temp);
    }
    else {
        Node* temp = findMinVal(node -> right);
        node -> key = temp -> key;
        free(temp);
    }
}

example tree:

Inorder traversal of the given tree:

20 30 40 50 60 70 80 

output and commands :

Delete 20
Inorder traversal of the modified tree 
0 30 40 50 60 70 80