Question

Program asks user to enter user name and password
If same user name exists in the primary index file, program does nothing and prints "User name already exist".
Otherwise, a new record is created of type admin, and written to "users.dat" file in fixed length record structure and the primary index file is updated .

Answer 1

#include<iostream>#include<string>#include<fstream>#include<list>#include<algorithm> using namespacestd; // filenamesconststring fnindex = "index.dat";conststring fnusers = "users.dat"; // list of usernameslist<string>users; boolAddUser (string username,string password) {    ofstream findex(fnindex,ios::app);    ofstream fusers(fnusers,ios::app);    string output;    bool res = true;     // primary index file is updated    if (findex.is_open()) {        output =username + "\n";        findex <<output;        findex.close();    } else {        res = false;    }        // new record is written"users.dat"    if (fusers.is_open()) {        output =username + "|" + "admin" + "|" +password + "\n";        fusers <<output;        fusers.close();    } else {        res = false;    }     returnres;} boolLoadUsernames() {    ifstream findex(fnindex);    string username;     // users are added to usernamelist    if (findex.is_open()) {        while (getline(findex,username)) {            users.push_back(username);        }        findex.close();        return true;    } else {        return false;    }} intmain() {    list<string>::iteratorpos;        string username;    string password;    bool newUser = true;     LoadUsernames();     while (newUser) {        cout << "Enterusername:" << endl;        cin >>username;         cout << "Enterpassword:" << endl;        cin >>password;         //username is checked         pos =find(users.begin(),users.end(),username);        if (pos== users.end()) {            AddUser(username,password);            newUser = false;        } else {            cout << "Username already exist" << endl;        }    }        return 0;}