How to Add or Subtract Days, Months, or Years from a Date in C#

Manipulating dates is a common task in C# applications, whether for scheduling, logging, or calculations.

The DateTime and DateOnly structures provide built-in methods to add or subtract days, months, years, hours, and minutes efficiently.

Adding and Subtracting Days

Use the AddDays method to modify a DateTime instance:

using System;

class Program
{
    static void Main()
    {
        DateTime today = DateTime.Now;
        DateTime nextWeek = today.AddDays(7);
        DateTime lastWeek = today.AddDays(-7);

        Console.WriteLine($"Today: {today:yyyy-MM-dd HH:mm}");
        Console.WriteLine($"Next Week: {nextWeek:yyyy-MM-dd HH:mm}");
        Console.WriteLine($"Last Week: {lastWeek:yyyy-MM-dd HH:mm}");
    }
}

Adding and Subtracting Months

Use the AddMonths method to adjust the month while automatically handling month-end variations:

DateTime currentDate = new DateTime(2025, 3, 31);
DateTime nextMonth = currentDate.AddMonths(1);
DateTime previousMonth = currentDate.AddMonths(-1);

Console.WriteLine($"Current Date: {currentDate:yyyy-MM-dd HH:mm}");
Console.WriteLine($"Next Month: {nextMonth:yyyy-MM-dd HH:mm}");
Console.WriteLine($"Previous Month: {previousMonth:yyyy-MM-dd HH:mm}");

Adding and Subtracting Years

Use the AddYears method to adjust the year, handling leap years automatically:

DateTime date = new DateTime(2024, 2, 29);
DateTime nextYear = date.AddYears(1);
DateTime previousYear = date.AddYears(-1);

Console.WriteLine($"Original Date: {date:yyyy-MM-dd HH:mm}");
Console.WriteLine($"Next Year: {nextYear:yyyy-MM-dd HH:mm}");
Console.WriteLine($"Previous Year: {previousYear:yyyy-MM-dd HH:mm}");

Adding and Subtracting Hours

Use the AddHours method to modify the hour component:

DateTime now = DateTime.Now;
DateTime inFiveHours = now.AddHours(5);
DateTime fiveHoursAgo = now.AddHours(-5);

Console.WriteLine($"Current Time: {now:yyyy-MM-dd HH:mm}");
Console.WriteLine($"In 5 Hours: {inFiveHours:yyyy-MM-dd HH:mm}");
Console.WriteLine($"5 Hours Ago: {fiveHoursAgo:yyyy-MM-dd HH:mm}");

Adding and Subtracting Minutes

Use the AddMinutes method to modify the minute component:

DateTime currentTime = DateTime.Now;
DateTime inThirtyMinutes = currentTime.AddMinutes(30);
DateTime thirtyMinutesAgo = currentTime.AddMinutes(-30);

Console.WriteLine($"Current Time: {currentTime:yyyy-MM-dd HH:mm}");
Console.WriteLine($"In 30 Minutes: {inThirtyMinutes:yyyy-MM-dd HH:mm}");
Console.WriteLine($"30 Minutes Ago: {thirtyMinutesAgo:yyyy-MM-dd HH:mm}");

Using DateOnly for Simpler Date Manipulation

For applications that don't require time components, DateOnly (introduced in .NET 6) provides a cleaner approach:

DateOnly today = DateOnly.FromDateTime(DateTime.Now);
DateOnly futureDate = today.AddDays(30);

Console.WriteLine($"Today: {today}");
Console.WriteLine($"30 Days Later: {futureDate}");

Conclusion

C# provides built-in methods for adjusting dates effortlessly. Whether working with DateTime or DateOnly, these functions ensure accurate date calculations, even when dealing with leap years, month-end scenarios, hours, and minutes.

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Related

Closing a SqlDataReader correctly prevents memory leaks, connection issues, and unclosed resources. Here’s the best way to do it.

Use 'using' to Auto-Close

Using using statements ensures SqlDataReader and SqlConnection are closed even if an exception occurs.

Example

using (SqlConnection conn = new SqlConnection(connectionString))
{
    conn.Open();
    using (SqlCommand cmd = new SqlCommand("SELECT * FROM Users", conn))
    using (SqlDataReader reader = cmd.ExecuteReader())
    {
        while (reader.Read())
        {
            Console.WriteLine(reader["Username"]);
        }
    } // ✅ Auto-closes reader here
} // ✅ Auto-closes connection here

This approach auto-closes resources when done and it is cleaner and less error-prone than manual closing.

⚡ Alternative: Manually Close in finally Block

If you need explicit control, you can manually close it inside a finally block.

SqlDataReader? reader = null;
try
{
    using SqlConnection conn = new SqlConnection(connectionString);
    conn.Open();
    using SqlCommand cmd = new SqlCommand("SELECT * FROM Users", conn);
    reader = cmd.ExecuteReader();

    while (reader.Read())
    {
        Console.WriteLine(reader["Username"]);
    }
}
finally
{
    reader?.Close();  // ✅ Closes reader if it was opened
}

This is slightly more error prone if you forget to add a finally block. But might make sense when you need to handle the reader separately from the command or connection.

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Slow initial load times can drive users away from your React application. One powerful technique to improve performance is lazy loading - loading components only when they're needed.

Let's explore how to implement this in React.

The Problem with Eager Loading

By default, React bundles all your components together, forcing users to download everything upfront. This makes navigation much quicker and more streamlined once this initial download is complete.

However, depending on the size of your application, it could also create a long initial load time.

import HeavyComponent from './HeavyComponent';
import AnotherHeavyComponent from './AnotherHeavyComponent';

function App() {
  return (
    <div>
      {/* These components load even if user never sees them */}
      <HeavyComponent />
      <AnotherHeavyComponent />
    </div>
  );
}

React.lazy() to the Rescue

React.lazy() lets you defer loading components until they're actually needed:

import React, { lazy, Suspense } from 'react';

// Components are now loaded only when rendered
const HeavyComponent = lazy(() => import('./HeavyComponent'));
const AnotherHeavyComponent = lazy(() => import('./AnotherHeavyComponent'));

function App() {
  return (
    <div>
      <Suspense fallback={<div>Loading...</div>}>
        <HeavyComponent />
        <AnotherHeavyComponent />
      </Suspense>
    </div>
  );
}

Route-Based Lazy Loading

Combine with React Router for even better performance:

import React, { lazy, Suspense } from 'react';
import { BrowserRouter, Routes, Route } from 'react-router-dom';

const Home = lazy(() => import('./pages/Home'));
const Dashboard = lazy(() => import('./pages/Dashboard'));
const Settings = lazy(() => import('./pages/Settings'));

function App() {
  return (
    <BrowserRouter>
      <Suspense fallback={<div>Loading...</div>}>
        <Routes>
          <Route path="/" element={<Home />} />
          <Route path="/dashboard" element={<Dashboard />} />
          <Route path="/settings" element={<Settings />} />
        </Routes>
      </Suspense>
    </BrowserRouter>
  );
}

Implement these techniques in your React application today and watch your load times improve dramatically!

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Storing passwords as plain text is dangerous. Instead, you should hash them using a strong, slow hashing algorithm like BCrypt, which includes built-in salting and resistance to brute-force attacks.

Step 1: Install BCrypt NuGet Package

Before using BCrypt, install the BCrypt.Net-Next package:

dotnet add package BCrypt.Net-Next

or via NuGet Package Manager:

Install-Package BCrypt.Net-Next

Step 2: Hash a Password

Use BCrypt.HashPassword() to securely hash a password before storing it:

using BCrypt.Net;

string password = "mySecurePassword123";
string hashedPassword = BCrypt.HashPassword(password);

Console.WriteLine(hashedPassword); // Output: $2a$12$...

Step 3: Verify a Password

To check a user's login attempt, use BCrypt.Verify():

bool isMatch = BCrypt.Verify("mySecurePassword123", hashedPassword);
Console.WriteLine(isMatch); // Output: True

Ensuring proper hashing should be at the top of your list when it comes to building authentication systems.

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