ошибка: множественное определение статического члена класса

#ifndef BANKACCOUNT_H
#define BANKACCOUNT_H
#include <string>
#include <ctime>
#include <iostream>
 
 
class bankAccount
{
 
public:
    
    bankAccount( std::string , std::string , double , double );  //Constructor
 
    static int id;                    //Static member (int named anything) used to automatically assign  account numbers during account
 
    void deposit(const double );      //Method add money to account
    void withdraw(const double );     ///Method take money out of account
    void getInterest(const double );  //Method balance times interest rate
    void updateBalance();              //Method adds interest amount to balance
 
    const std::string getAccountHolderName() const;      //Method that returns the name of the account owner
    const int getAccountNumber()             const;      //Method that returns the account number
    const std::string getAccountType()       const;      //Method that returns the type number
    const double getBalance()                const;      //Method that returns the account balance
    const double getInterestRate()           const;      //Method that returns the account's interest rate
 
 
   const void print()                       const;      //Method that returns all account information
 
 
 
private:
 
    std::string mName{""};         //Account holders name
    int mAccountNumber{0};         //Account number
    std::string mAccountType{""};  //Account type
    double mBalance{0.0};          //Balance
    double mInterestRate{0.0};     //Interest rate
 
 
 
 
};
 int bankAccount::id = 0;  //Initialization static member
 
#endif // BANKACCOUNT_H

int bankAccount::id = 0;

class bankAccount
{
 
public:
    
    bankAccount( std::string , std::string , double , double );  //Constructor
    //!!!!
    inline static int id = 0;                    //Static member (int named anything) used to automatically assign  account numbers during account
 ///..................
};
//!!! это тогда  не нужно: int bankAccount::id = 0;  //Initialization static member