exercise with fstream

[ntrncx]

hey all

i am studying from a book,and i have to do an exercise.
i dont want code or anything i want tip or someone explain me how to do it.
i have a oldmast.dat file with some records a trans.dat file with records and i have to update the oldmast.dat to a new file,i did that. the files are sequential.

the exercise after i do that asks to be able to solve if an transcation file has 2 entrys with same account.

my code is:

#include <iostream>
#include <fstream>
#include <cstdlib>
using namespace std;

void update(int,double &,ifstream &);
bool check(int,ifstream &);

int main()
{
    ifstream inOldMaster("oldmast.dat",ios::in);
    ifstream inTransaction("trans.dat",ios::in);
    ofstream outNewMaster("newMast.txt",ios::out);
    
    if(!outNewMaster || !inOldMaster || !inTransaction)
    {
        cout<<"file could not be opened\n";
        exit(1);
    }
    
    int accountNumber;
    string first,last;
    double currentBalance;
    
    while(inTransaction>>accountNumber>>currentBalance)
    {
        if(check(accountNumber,inOldMaster))
            cout<<"Unmatched transaction record for account number "<<accountNumber<<endl;
    }
    
    inTransaction.close();
    inOldMaster.close();
    inOldMaster.open("oldmast.dat",ios::in);
    inTransaction.open("trans.dat",ios::in);    
    
    while(inOldMaster>>accountNumber>>first>>last>>currentBalance)
    {
        update(accountNumber,currentBalance,inTransaction);
        outNewMaster<<accountNumber<<' '<<first<<' '<<last<<" $"<<currentBalance<<endl;
    }
    cout<<"input Completed\n";        
}

void update(int account,double &balance,ifstream &trans ) {
    double ammount;
    int accountNumber;
    while(trans>>accountNumber>>ammount) 
    {
        if(account==accountNumber)
        {
            balance+=ammount;
            break;
        }     
    }
}

bool check(int account,ifstream &master) {
    int accountNum;
    double balance;
    string first,last;
    
    while(master>>accountNum>>first>>last>>balance)
    {
        if(accountNum==account)
            return false;        
    }
    return true;
}

the 2 question is can i do write something else instead of close and open files?lines 31-34

and at sequential files how i can fix if an entry exist more than 2 times?

example:
lets say the file trans2.dat has the following
Account Ammount
300 83.89
700 80.78
700 1.53

i am almost sure that i have to use seekg/seekp or tellp/tellg but i ahvent quite understand how to use them.

thanks for your time
someone that studies c++ for hobby

[ratatat]

dont declare the ifstream stuff in a function, try declaring everything separate.
in other words, please don't include any arguments in your functions or methods. that wawy things should be clearer. goodluck