声明一个银行帐号类BankAccount，成员变量为账户号，户主姓名，户主身份证号，账户余额，该类有三个构造方法，分别为BankAccount（），BankAccount（账户号，户主姓名，身份证号）（账户余额默认为0），BankAccount（账户号，户主姓名，身份证号，账户余额）。分别使用三个构造函数建立三个对象，并打印输出三个账户信息。-Declare a bank account class BankAccount, member variables for account number, head of a household name, head of the household id number, account balance, the three construction method, respectively BankAccount (), BankAccount (account number, head of a household name, id number) (account balance the default is 0), BankAccount (account number, head of a household name, id number, account balance). Separately using three structure function to establish three object, and print output three account information.