Problems reading and writing char and int type.

Hello experts,

I need to understand what I am missing here please.
I have a program that uses code to auto generates customer IDs on account creation. Here is how I achieve this;

I have a file called account.dat which contains a figure, for example 99.
I get this figure 99, and add 1 to it to get 100. 100 is the new account number generated, and 100 is returned to account.dat.

To save data, I am writing to a binary file like so;

                         dataIn.write((char*) (&account),sizeof (account));

In order to be able to write the new account number to file along with other customer details, i convert the accountnumber to char using the following code;
   
                         char AccountNumberE[20];//global variable
                         itoa (AccountNumber, AccountNumberE, 10);/*convert int AccountNumber to char.


see full code below;

char* Customer::returnAccountNumber()
{
//generate new account number
            inAccountNum.open("account.dat", ios::in);/*assign file to input stream from
                                                                          account number.*/


            if (inAccountNum.is_open())//if file is open
            {
                  inAccountNum >> AccountNumber; //get account number from account.dat
                  inAccountNum.close();
            }
            else //otherwise, if file is closed
            {
                  cout << "the file has not been open"; //display information
            }

            AccountNumber = AccountNumber + 1;//add one to account number
            itoa (AccountNumber, AccountNumberE, 10);/*convert int AccountNumber to char,
                                                                         to prevent memory errors when reading data.*/

            outAccountNum.open("account.dat"); //open account.dat for output
            outAccountNum << AccountNumber;//replace account number in account.dat with new figure for future use.
            outAccountNum.close();//close account.dat
            return AccountNumberE;



This function is then called elsewhere in my program like so;
void Customer::add(int flag)
{

      while (!cin.get()) {};

      if (flag==1)
      {

                      Customer accountnumber;
            do
            {      
            cout << "\n\n NEW CUSTOMER ACCOUNT NUMBER GENERATED:"
                                << accountnumber.returnAccountNumber() << "\n";
            }while (!stringCheck(accountnumber.returnAccountNumber(),0));//checks that acceptable input is received.

                 }


Now the problem I am having is that the following line;

                          cout << "\n\n NEW CUSTOMER ACCOUNT NUMBER GENERATED:"

 outputs the account number correctly, but when I read from file like so,

void Customer::display(void)
{
      cout << setiosflags(ios::left)<<setw(5)<<AccountNumberE<< setw(20)<<name;
      cout << setw(25)<<address<<setw(15)<<telephone<<setw(10)<<lastMeterReading<<setw(10)<<type<<"\n";
}

 the is no data for account number and if I do the following;

                         int i = atoi(AccountNumberE);//convert customer ID from char to int


to convert back to int before displaying, I get 0 for account number.

I don't know where the problem is occuring, it appears the ID isn't being written to the file. Because if I then switch the add(intflag) function for account number so the the user inputs it manually, then there is not problem, the figure is written to and read from file.

However the requirement for the program ia that it autogenerates account number.

Any help is appreciated.