computers connected to the same WiFi network in C#

Here is sample code that uses SendPingAsync :

using System.Net;
using System.Net.NetworkInformation;

public static async Task> ScanNetwork(string subnet)
{
    var activeHosts = new List();
    var tasks = new List();
    
    for (int i = 1; i < 255; i++)
    {
        string ip = $"{subnet}.{i}";
        tasks.Add(Task.Run(async () =>
        {
            using var ping = new Ping();
            try
            {
                var reply = await ping.SendPingAsync(ip, 1000);
                if (reply.Status == IPStatus.Success)
                {
                    lock (activeHosts)
                    {
                        activeHosts.Add(ip);
                    }
                }
            }
            catch { }
        }));
    }
    
    await Task.WhenAll(tasks);
    return activeHosts;
}
  

For the subnet parameter, you need to pass the first three octets of your local IP address range (without the last number). The following can get that:

using System.Net;
using System.Net.Sockets;
using System.Net.NetworkInformation;

public static string GetLocalSubnet()
{
    var host = Dns.GetHostEntry(Dns.GetHostName());
    
    foreach (var ip in host.AddressList)
    {
        // Get IPv4 address that's not loopback
        if (ip.AddressFamily == AddressFamily.InterNetwork && 
            !IPAddress.IsLoopback(ip))
        {
            // Extract first three octets (e.g., "192.168.1" from "192.168.1.100")
            string[] octets = ip.ToString().Split('.');
            return $"{octets[0]}.{octets[1]}.{octets[2]}";
        }
    }
    
    return "192.168.1"; // Fallback
}

Since you specify WiFi explicitly I am not sure if you only want devices connected using WiFi. Many people say WiFi when they mean to say network. Networks can include devices using ethernet instead of WiFi. If you only want devices connected using WiFi then you will need to add code to filter for that.

For Windows, you can alternatively use the IP Helper API through P/Invoke but that is probably more than what you want to do.

Try the below method

On Windows, the most common practical is:

Ping sweep the local subnet ? read the ARP table ? resolve hostnames

How it works (high level)

1. Get your local IP + subnet

2. Ping every IP in that subnet (fast, parallel)

3. Read the ARP table (arp -a)

4. Match IP ? MAC addresses

5. (Optional) Resolve hostnames

C# console program sample code:

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Net;
using System.Net.NetworkInformation;
using System.Net.Sockets;
using System.Text.RegularExpressions;
using System.Threading.Tasks;

class Program
{
    static async Task Main()
    {
        Console.WriteLine("Scanning network...\n");

        await PingSubnet();

        var devices = ReadArpTable();

        foreach (var d in devices)
        {
            Console.WriteLine($"{d.IP,-15} {d.Mac,-18} {d.Host}");
        }

        Console.WriteLine("\nDone.");
        Console.ReadKey();
    }

    static async Task PingSubnet()
    {
        string localIP = GetLocalIPv4();
        string baseIP = localIP.Substring(0, localIP.LastIndexOf('.') + 1);

        var tasks = new List();

        for (int i = 1; i < 255; i++)
        {
            string ip = baseIP + i;
            tasks.Add(Task.Run(async () =>
            {
                try
                {
                    using var ping = new Ping();
                    await ping.SendPingAsync(ip, 100);
                }
                catch { }
            }));
        }

        await Task.WhenAll(tasks);
    }

    static string GetLocalIPv4()
    {
        return Dns.GetHostEntry(Dns.GetHostName())
            .AddressList
            .First(ip => ip.AddressFamily == AddressFamily.InterNetwork)
            .ToString();
    }

    static List<(string IP, string Mac, string Host)> ReadArpTable()
    {
        var list = new List<(string, string, string)>();

        var p = new Process
        {
            StartInfo = new ProcessStartInfo
            {
                FileName = "arp",
                Arguments = "-a",
                RedirectStandardOutput = true,
                UseShellExecute = false,
                CreateNoWindow = true
            }
        };

        p.Start();
        string output = p.StandardOutput.ReadToEnd();
        p.WaitForExit();

        var regex = new Regex(
            @"(?\d+\.\d+\.\d+\.\d+)\s+(?[a-f0-9\-]{17})",
            RegexOptions.IgnoreCase
        );

        foreach (Match m in regex.Matches(output))
        {
            string ip = m.Groups["ip"].Value;
            string mac = m.Groups["mac"].Value;
            string host;

            try
            {
                host = Dns.GetHostEntry(ip).HostName;
            }
            catch
            {
                host = "Unknown";
            }

            list.Add((ip, mac, host));
        }

        return list;
    }
}

I don't think it is possible via .NET/C#. What you can do is to ping IPs in the network.

var ping = new Ping();
var resp = await ping.SendPingAsync("YOUR IP HERE..");
Console.WriteLine(resp.Status.ToString());

If it responds, device is reachable.