ATM using file handling in C++

In this article, the task is to implement an ATM with functions like add, delete, search, and update users using file handling in C++.  

File handling:

• File handling is used to store the output of a program in a file.
• In C++, files use three classes fstream, ifstream, ofstream available in fstream header file for file handling.

Some Important Instructions:

1. The password for Admin login is 1234.
2. Initially, the file is empty make sure to first log in as admin and add a user, and then login as a user.

Approach:

• Select user type and input password. 
• In the given menu, select the basic operation and enter the details in the operations like add, delete, search and update users.
• After performing all the functions and operations, exit from the ATM system.
• All the file operations are done in a file named aaa.txt, where the data is written using ofstream mode and can be read using ifstream mode.
• After this, the file must be closed using <filename>.close().

Below is the implementation of the above approach:

C++

// C++ code to implement an ATM and
// its basic functions
#include <fstream>
#include <iostream>
#include <limits>
#include <string.h>
#include <unistd.h>
using namespace std;

// Class ATM to get user details
class atm {
private:
    char username[30];
    int password;
    int balance;

public:
    char* usernames(void)
    {
        // Return username
        return the username;
    }

    int passwords(void)
    {
        // Return the password
        return password;
    }

    // Function to get the data
    void getData(void)
    {
        cin.ignore(
            numeric_limits<streamsize>::max(),
            '\n');
        cout << "\nEnter username:";

        cin.getline(username, 30);
        cout << "\nEnter 4-digit "
             << "password:";

        cin >> password;
        cin.ignore(
            numeric_limits<streamsize>::max(),
            '\n');
        cout << "\nEnter initial"
             << " balance:";

        cin >> balance;
        cin.ignore(
            numeric_limits<streamsize>::max(),
            '\n');
    }

    // Function displaying the data
    void showData(void)
    {
        cout << "Username:" << username
             << ", Password:" << password
             << ", Balance:" << balance
             << endl;
    }

    // Member Functions
    int adduser();
    int viewallusers();
    int deleteuser(char*);
    void updateuserasdeposit(char*);
    void updateuseraswithdraw(char*);
    int searchspecificuser(char*, int);
    int searchallusertodisplay(char*);
};

// Function to implement functionality
// of ATM User
void atmUser()
{
    atm a;

    char uname[30];
    int pass, ch, ch1, ch2, found = 0;

mainmenu:

    // System("cls");
    cout << "\nWelcome to GeeksforGeeks ATM";
    cout << "\nLogin as :\n1. Admin\n2."
         << " User\n3. "
            "Exit\nChoose one : ";
    cin >> ch;

    switch (ch) {
    case 1:
    rerun:
        // System("cls");
        cout << "\nEnter details to"
             << " login as Admin\n";
        cout << "\nEnter password:";
        cin >> pass;
        if (pass == 1234) {
        admin:
            // System("cls");
            cout << "\nWelcome to"
                 << " Admin Menu";
            cout << "\n1. Add User\n2."
                 << " Delete User\n3. "
                    "View All User\n4. "
                 << "Exit";
            cout << "\nSelect one : ";
            cin >> ch1;
            switch (ch1) {
            case 1:
                a.adduser();
                goto admin;

            case 2:
                cout << "\nEnter the "
                     << "Username to be "
                        "deleted : ";
                cin.ignore(
                    numeric_limits<streamsize>::max(),
                    '\n');
                cin.getline(uname, 30);
                a.deleteuser(uname);
                goto admin;

            case 3:
                a.viewallusers();
                // sleep(4);
                goto admin;

            case 4:
                break;
            }
        }
        else {
            cout << "\nDetails are "
                 << "incorrect ! Please"
                    " try again";
            cin.get();
            goto rerun;
        }
        goto mainmenu;

    case 2:
        // System("cls");
        cout << "\n Enter details to"
             << " login as User\n";

        cin.ignore(
            numeric_limits<streamsize>::max(),
            '\n');
        cout << "Enter username:";
        cin.getline(uname, 30);
        cout << "\nEnter password:";

        cin >> pass;
        found = a.searchspecificuser(
            uname, pass);

        if (found) {
        user:
            // System("cls");
            cout << "\nWelcome "
                 << uname;
            cout << "\nWelcome to"
                 << " User Menu";
            cout << "\n1. Deposit\n2."
                 << " Withdraw\n3. View "
                    "Account\n4. "
                 << "Exit\nEnter your choice:";
            cin >> ch2;

            switch (ch2) {
            case 1:
                a.updateuserasdeposit(uname);
                goto user;
            case 2:
                a.updateuseraswithdraw(uname);
                goto user;
            case 3:
                a.searchallusertodisplay(uname);
                // sleep(4);
                goto user;
            case 4:
                cout << "Thank you";
                break;
            }
        }
        else {
            cout << "\nNo account found"
                 << " with username "
                    ":(\n\nHit ENTER to continue "
                 << uname;
            cin.get();
        }
        goto mainmenu;

    case 3:
        cout << "\nThankyou for "
             << "banking with "
             << "GeeksforGeeks";
        cin.get();
        break;
    }
}

// Function to add user
int atm::adduser()
{
    atm a;

    ofstream file;

    // Open file in write mode
    file.open("aaa.txt",
              ios::out | ios::app);
    if (!file) {
        cout << "Error in creating "
             << "file.." << endl;
        return 0;
    }

    // Read from user
    a.getData();

    // Write into file
    file.write((char*)&a, sizeof(a));

    // Close the file
    file.close();

    return 0;
}

// View Users
int atm::viewallusers()
{

    atm a;

    ifstream file1;

    // Open file in read mode
    file1.open("aaa.txt", ios::in);
    if (!file1) {
        cout << "Error in opening file..";
        return 0;
    }

    // Read data from file
    file1.read((char*)&a, sizeof(a));
    while (!file1.eof()) {

        // Display data on monitor
        a.showData();
        file1.read((char*)&a, sizeof(a));
    }

    // Close the file
    file1.close();
    return 0;
}

// Function to delete the user
int atm::deleteuser(char* uname)
{

    atm a;

    fstream original, temp;
    original.open("aaa.txt", ios::in);
    if (!original) {
        cout << "\nfile not found";
        return 0;
    }
    else {
        temp.open("temp.txt",
                  ios::out | ios::app);
        original.read((char*)&a, sizeof(a));

        // Till end of file is reached
        while (!original.eof()) {

            if (!strcmp(a.usernames(),
                        uname)) {
                cout << "data found "
                     << "and deleted\n"
                     << a.username
                     << "\n";
            }
            else {
                temp.write((char*)&a,
                           sizeof(a));
            }

            original.read((char*)&a,
                          sizeof(a));
        }

        original.close();
        temp.close();
        remove("aaa.txt");
        rename("temp.txt", "aaa.txt");
        a.viewallusers();
    }
    return 0;
}

// Function to update user by
// depositing money
void atm::updateuserasdeposit(char* uname)
{

    atm a;
    fstream file, temp;
    file.open("aaa.txt",
              ios::in | ios::out | ios::ate);
    temp.open("temp.txt",
              ios::out | ios::app);
    file.seekg(0);
    file.read((char*)&a, sizeof(a));

    // Till end of the file
    while (!file.eof()) {
        if (!strcmp(a.usernames(), uname)) {
            int b;

            cout << "\nEnter amount "
                 << "to deposit:";
            cin >> b;
            a.balance = a.balance + b;
            cout << "\nBalance is:"
                 << a.balance;
            temp.write((char*)&a, sizeof(a));
        }
        else {
            temp.write((char*)&a, sizeof(a));
        }
        file.read((char*)&a, sizeof(a));
    }
    file.close();
    temp.close();
    remove("aaa.txt");
    rename("temp.txt", "aaa.txt");
}

// Function to update user by
// depositing withdrawing money
void atm::updateuseraswithdraw(char* uname)
{

    atm a;
    fstream file, temp;
    file.open("aaa.txt",
              ios::in | ios::out | ios::ate);
    temp.open("temp.txt",
              ios::out | ios::app);
    file.seekg(0);
    file.read((char*)&a, sizeof(a));

    // Till end of file is reached
    while (!file.eof()) {
        if (!strcmp(a.usernames(), uname)) {
            int b;
            cout << "\nEnter amount "
                 << "to withdraw:";
            cin >> b;
            if (a.balance < b) {
                cout
                    << "\nInsufficient "
                    << "balance to withdraw";
            }
            else {
                a.balance = a.balance - b;
                temp.write((char*)&a,
                           sizeof(a));
                cout << "\nBalance is:"
                     << a.balance;
            }
        }
        else {
            temp.write((char*)&a,
                       sizeof(a));
        }
        file.read((char*)&a, sizeof(a));
    }

    // Close the file
    file.close();
    temp.close();
    remove("aaa.txt");
    rename("temp.txt", "aaa.txt");
}

// Search user
int atm::searchspecificuser(
    char* uname, int pass)
{
    atm a;
    fstream f;

    // Open the file
    f.open("aaa.txt", ios::in);
    if (!f) {
        cout << "Error in opening file..";
        return 0;
    }

    // Read data from file
    f.read((char*)&a, sizeof(a));
    while (!f.eof()) {

        if (!strcmp(a.usernames(), uname)) {
            if (a.passwords() == pass) {
                return 1;
            }
        }
        f.read((char*)&a, sizeof(a));
    }

    // Close the file
    f.close();
    return 0;
}

// Search specific user
int atm::searchallusertodisplay(
    char* uname)
{
    atm a;
    fstream file1;

    // Open the file
    file1.open("aaa.txt", ios::in);
    if (!file1) {
        cout << "Error in opening file..";
        return 0;
    }

    // Read data from file
    file1.read((char*)&a, sizeof(a));
    while (!file1.eof()) {
        if (!strcmp(a.usernames(), uname)) {
            a.showData();
            return 0;
        }
        file1.read((char*)&a, sizeof(a));
    }

    // Close the file
    file1.close();
    return 0;
}

// Driver Code
int main()
{
    // Function Call
    atmUser();

    return 0;
}

Output: