if (mysql_query(&mysql, "delete from books where books_id = 14")) { cout << "Error: Query[删除成功] fail." << endl; break; } cout << "Query[delete] success." << endl;将这段c++代码中的books_id换成可输入的变量

可以将变量作为参数传递给SQL语句，示例代码如下：

int book_id;
cout << "请输入要删除的书籍ID：";
cin >> book_id;

string query = "DELETE FROM books WHERE books_id = " + to_string(book_id);

if (mysql_query(&mysql, query.c_str())) {
    cout << "Error: Query[删除成功] fail." << endl;
    break;
}
cout << "Query[delete] success." << endl;

需要注意的是，使用变量构造SQL语句时需要避免SQL注入攻击，可以使用参数化查询来提高安全性。