输出类型类的向量

上一个问题中，这个问题有更多的代码： C++ 将数据输入私有向量时遇到问题（无效使用）

我正在尝试输出"帐户"类型的向量

帐户：

class Account
{
    string firstName;
    string lastName;
    string accountPass;
    int accountID;
    float accountBalance;
private:
    int depositAmount;
    int withdrawAmount;
public:
    static Account createAccount( int, float, string, string, string ); //creates new account
    void deposit( int );    //deposits money into account
    void withdraw(int);     //withdrawals money from account
    int retdeposit() const; //function to return balance amount
    friend class BankingSystem;
}; //end of class Account

这是我声明向量的方式： std::vector<Account> accounts_;

这是我尝试将其打印到屏幕上的方式：

for(int i=0; i < accounts_.size(); i++)
{     cout<< accounts_[i] <<endl;   }

但是我收到此错误"二进制表达式的操作数无效"。

当前代码;

class BankingSystem
{
int accountID;
char fileName;
private:
std::vector<Account> accounts_;
public:
void addAccount();
void storeAccount( Account );
void deleteAccount();
void accountInquiry();
void saveAccounts();
void loadAccountsFromFile();
friend class Account;
friend std::ostream& operator << (std::ostream&, const Account&);
}; // end of class BankingSystem
#endif

std::ostream& operator << (std::ostream& os, const Account& acc)
{
// output members to os
return os;
}
void BankingSystem::addAccount()
{
int ID;
float balance;
std::string pass, first, last;
cout << "nt Enter the Account ID: ";
cin >> ID;
cout << "nt Enter the passcode: ";
cin >> pass;
cout << "nt Enter Client's first name: ";
cin >> first;
cout << "nt Enter Client's last name: ";
cin >> last;
cout << "nt Enter starting balance: ";
cin >> setw(6) >> balance;
storeAccount( Account::createAccount( ID, balance, pass, first, last ) );
return;
}
//function gets data from createAccount
void BankingSystem::storeAccount( Account newAccountToAdd )
{
//append to vector "accounts_"
accounts_.push_back(newAccountToAdd);
}
void BankingSystem::deleteAccount()
{
cout << "nEnter The Account ID: ";
cin >> accountID;

}
void BankingSystem::accountInquiry()
{
int n;
cout << "nt Enter The Account ID (-1 for all): ";
cin >> n;
//cout << accounts_.size();
if (n == -1)
{
    cout << "nt List of all Accounts; (" << accounts_.size() << ") TOTAL: ";
    for(int i=0; i < accounts_.size(); i++)
    {     
        cout<< accounts_[i] << endl;   
    }
}
else
{
    cout << "nt Listing Account: " << n;
    cout << "nt I should search the vector for the ID you input";
}
}