如何在C中更新全局链表？

typedef struct Node {
    int data;
    struct Node* next;
} Node;

Node* head = NULL;

void insertNode(int value) {
    Node* newNode = (Node*)malloc(sizeof(Node));
    newNode->data = value;
    newNode->next = NULL;
    
    if (head == NULL) {
        head = newNode;
    } else {
        Node* current = head;
        while (current->next != NULL) {
            current = current->next;
        }
        current->next = newNode;
    }
}

void deleteNode(int value) {
    if (head == NULL) {
        return;
    }
    
    Node* current = head;
    Node* previous = NULL;
    
    while (current != NULL && current->data != value) {
        previous = current;
        current = current->next;
    }
    
    if (current == NULL) {
        return;
    }
    
    if (previous == NULL) {
        head = current->next;
    } else {
        previous->next = current->next;
    }
    
    free(current);
}

void updateNode(int oldValue, int newValue) {
    Node* current = head;
    
    while (current != NULL) {
        if (current->data == oldValue) {
            current->data = newValue;
            break;
        }
        current = current->next;
    }
}

void printList() {
    Node* current = head;
    
    while (current != NULL) {
        printf("%d ", current->data);
        current = current->next;
    }
    printf("\n");
}

int main() {
    insertNode(1);
    insertNode(2);
    insertNode(3);
    printList();  // 输出：1 2 3
    
    deleteNode(2);
    printList();  // 输出：1 3
    
    updateNode(3, 4);
    printList();  // 输出：1 4
    
    return 0;
}