async / await

// Define an async method (no return value)
async Task MethodName()
{
    await asyncOperation;
}

// Define an async method (with return value)
async Task<T> MethodName()
{
    T result = await asyncOperation;
    return result;
}

// Call an async method
await MethodName();
T value = await MethodName();

using System;
using System.Net.Http;
using System.Threading.Tasks;

// Define an async method with no return value.
async Task PrintGreetingAsync(string name)
{
    await Task.Delay(100); // Simulates a 100ms delay.
    Console.WriteLine($"Hello, {name}!");
}

// Define an async method with a return value.
async Task<int> AddAsync(int a, int b)
{
    await Task.Delay(50);  // Simulates an async operation.
    return a + b;
}

// Run multiple async operations sequentially.
async Task RunSequentialAsync()
{
    await PrintGreetingAsync("Alice");
    await PrintGreetingAsync("Bob");
    int result = await AddAsync(3, 4);
    Console.WriteLine($"3 + 4 = {result}");
}

// Entry point (.NET 5 and later allow async Main)
await RunSequentialAsync();
Console.WriteLine("Done");

Using async/await lets you wait for time-consuming operations (such as network or file I/O) to complete without blocking the thread. At each await point, the thread is released and the remaining code resumes after the operation finishes.

Do not use async void outside of event handlers. Exceptions thrown inside an async void method cannot propagate to the caller, making them extremely difficult to debug. Always return async Task instead.

To run multiple async operations in parallel, see Task.Run() / Task.Delay() / Task.WhenAll(). For exception handling inside async methods, see Exception Handling and Async.