How can I update record in file in c++?

void dep_with(int e, int f)
{
    int amt;
    int recordFind=0;
    account ac;
    ifstream updatedata("E:\\c++ Project\\final thoughts\\my.dat", ios::in|ios::out);
    while(updatedata.read((char*) &ac, sizeof(ac)) && recordFind==0)
    {
        if(ac.get_account()==e)
        {
            ac.view_account();
            if(f==1)
            {
                cout<<"\nEnter the amount to be deposited";
                cin>>amt;
                ac.deposits(amt);
            }
            if(f==2)
            {
                cout<<"\nEnter the amount to be withdraw";
                cin>>amt;
                ac.withdrawls(amt);
            }
            int pos=(-1)*sizeof(ac);
            ofstream updatedata("E:\\c++ Project\\final thoughts\\my.dat", ios::in|ios::out|ios::app);
            updatedata.seekp(pos,ios::cur);
            updatedata.write((char*) &ac, sizeof(ac));
            cout<<"\n\n\tRecord Updated";
            recordFind=1;
        }

    }
    updatedata.close();
    if(recordFind==0)
    {
        cout<<"\n\nRecord not Found";
    }
}