Async / Await Example

program.cs

using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Text.Json;
using System.Threading.Tasks;



public class Program
{
    private record Temprature(string Source, double Temperature);
    
    //Register at OpenWeatherMap and get your API key.
    private const string ApiKey = "YOUR_API_KEY"; 
    private static readonly HttpClient HttpClient = new();

    private static async Task Main(string[] args)
    {
        Console.WriteLine("Fetching weather temperatures from multiple sources...\n");

        // Define tasks for different weather sources
        List<Task<Temprature>> weatherTasks = new()
        {
            GetWeatherFromSourceAAsync(),
            GetWeatherFromSourceBAsync(),
            GetWeatherFromSourceCAsync(),
            GetRealWeatherFromOpenWeatherMapAsync("New York") // Real weather source
        };

        // Example 1: Wait for all sources to complete
        Console.WriteLine("Waiting for all sources to complete:\n");
        var allResults = await Task.WhenAll(weatherTasks);
        foreach (var result in allResults)
        {
            Console.WriteLine($"Source: {result.Source}, Temperature: {result.Temperature}°C");
        }

        // Example 2: Process the first result that completes
        Console.WriteLine("\nWaiting for the first source to complete:\n");
        var firstResult = await Task.WhenAny(weatherTasks);
        var completedResult = await firstResult; // Await the completed task
        Console.WriteLine($"Source: {completedResult.Source}, Temperature: {completedResult.Temperature}°C\n");

        Console.WriteLine("Done!");
    }

    // Simulate getting weather from Source A
    private static async Task<Temprature> GetWeatherFromSourceAAsync()
    {
        await Task.Delay(2000); // Simulate network delay
        return new Temprature("Source A", 25.3);
    }

    // Simulate getting weather from Source B
    private static async Task<Temprature> GetWeatherFromSourceBAsync()
    {
        await Task.Delay(1000); // Simulate network delay
        return new Temprature("Source B", 26.1);
    }

    // Simulate getting weather from Source C
    private static async Task<Temprature> GetWeatherFromSourceCAsync()
    {
        await Task.Delay(1500); // Simulate network delay
        
        return new Temprature("Source C", 24.8);
    }

    // Real weather source using OpenWeatherMap API
    static async Task<Temprature> GetRealWeatherFromOpenWeatherMapAsync(string city)
    {
        var url = $"https://api.openweathermap.org/data/2.5/weather?q={city}&units=metric&appid={ApiKey}";
        try
        {
            var response = await HttpClient.GetAsync(url);
            response.EnsureSuccessStatusCode();
            var json = await response.Content.ReadAsStringAsync();
            using var doc = JsonDocument.Parse(json);
            var temperature = doc.RootElement.GetProperty("main").GetProperty("temp").GetDouble();
            return new Temprature(city, temperature);
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error fetching weather for {city}: {ex.Message}");
            return new Temprature(city, double.NaN);
        }
    }
}