Group
File Handling in C#
Objective
1. Upon starting the program, it will check if a file named "friends.db" exists.
2. If the file exists, it will load the list of friends from the file.
3. The user can add friends to the database during the session.
4. Upon exiting the session, the program will save the updated friends list to "friends.db".
5. The next time the program starts, it will load the data from "friends.db" automatically.
Expand the "friends database", so that it loads data from file at the beginning of each session (if the file exists) and saves the data to file when the session ends. Therefore, the data entered in a session must be available for the next session.
Example C# Exercise
Show C# Code
using System;
using System.Collections.Generic;
using System.IO;
class Friend
{
public string Name { get; set; }
public int Age { get; set; }
// Constructor to initialize a new Friend object
public Friend(string name, int age)
{
Name = name;
Age = age;
}
// Method to convert Friend object to a string format suitable for saving to a file
public override string ToString()
{
return $"{Name},{Age}";
}
}
class FriendsDatabase
{
private List friends;
// Constructor to initialize the friends list
public FriendsDatabase()
{
friends = new List();
}
// Method to load friends data from a file
public void LoadFromFile(string fileName)
{
if (File.Exists(fileName))
{
// Read all lines from the file
string[] lines = File.ReadAllLines(fileName);
// Iterate through each line and create a new Friend object
foreach (var line in lines)
{
string[] parts = line.Split(',');
if (parts.Length == 2)
{
string name = parts[0];
int age = int.Parse(parts[1]);
friends.Add(new Friend(name, age));
}
}
}
}
// Method to save friends data to a file
public void SaveToFile(string fileName)
{
List lines = new List();
// Convert each friend object to a string and add to the list
foreach (var friend in friends)
{
lines.Add(friend.ToString());
}
// Write all lines to the file
File.WriteAllLines(fileName, lines);
}
// Method to display all friends
public void DisplayFriends()
{
Console.WriteLine("Friends List:");
foreach (var friend in friends)
{
Console.WriteLine($"Name: {friend.Name}, Age: {friend.Age}");
}
}
// Method to add a new friend
public void AddFriend(string name, int age)
{
friends.Add(new Friend(name, age));
}
}
class Program
{
static void Main(string[] args)
{
// Create an instance of the FriendsDatabase class
FriendsDatabase database = new FriendsDatabase();
// File name where friends data will be saved and loaded from
string fileName = "friends.db";
// Step 1: Load data from file if it exists
database.LoadFromFile(fileName);
// Step 2: Display the current friends list
database.DisplayFriends();
// Step 3: Ask user if they want to add a new friend
Console.WriteLine("\nDo you want to add a new friend? (yes/no): ");
string response = Console.ReadLine().ToLower();
if (response == "yes")
{
Console.Write("Enter the friend's name: ");
string name = Console.ReadLine();
Console.Write("Enter the friend's age: ");
int age = int.Parse(Console.ReadLine());
// Add the new friend to the database
database.AddFriend(name, age);
}
// Step 4: Save updated data to file when the session ends
database.SaveToFile(fileName);
// Step 5: Display the final list of friends
Console.WriteLine("\nUpdated Friends List:");
database.DisplayFriends();
}
}
Output
//If the program is run and the file friends.db contains the following:
Alice,25
Bob,30
//The output will be:
Friends List:
Name: Alice, Age: 25
Name: Bob, Age: 30
Do you want to add a new friend? (yes/no): yes
Enter the friend's name: Charlie
Enter the friend's age: 22
Updated Friends List:
Name: Alice, Age: 25
Name: Bob, Age: 30
Name: Charlie, Age: 22