Add calendar days.
Use DateOnly for a date without a time zone in C#.
using System;
using System.IO;
using System.Linq;
using System.Collections.Generic;
using System.Text.Json;
Console.WriteLine(new DateOnly(2026, 1, 30).AddDays(3).ToString("yyyy-MM-dd"));Expected output EXAMPLE
2026-02-02
Details
Use Program.cs in a .NET 8 console project (dotnet new console --framework net8.0), then dotnet run. Uses only the .NET standard libraries.
Tested on Ubuntu 24.04.5 LTS · · 8.0.425 · libc6 2.39-0ubuntu8.9
Test inputs, results and environment
The exact published code ran in a dedicated Linux test container with prepared inputs. Unprivileged snippet process, external networking disabled, read-only root filesystem, and a fresh temporary working directory. Fixtures and output records are isolated from the application database. Testing covers this example and its stated checks, not every input, operating system, or runtime version. The Linux container shares its host's kernel; this is not a native Windows test.
- Architecture / host kernel
- x86_64 / 6.18.54.1-microsoft-standard-WSL2
- Snippet identity / locale
- uid=65534, gid=65534 (unprivileged) / C.UTF-8
- Interpreter invocation
dotnet build --no-restore && dotnet out/csharp.dll- Container image ID
sha256:32dc2d998158b6554c99b73b533f423696a0f3e31e8cbea9db10b5eee9a2fadd- Code SHA-256
99b9a1295259df02817048ac93bedd13f7c1c02b68bf74a7e584757f170aa083- Dependencies
- libc6 2.39-0ubuntu8.9
Test input setup
These are the prepared inputs used by the test harness. See Details above for the prerequisites and how to run this example.
# No input files required.
Observed standard output
2026-02-02
Exit code: 0. Standard error: empty. Validation: Exact stdout comparison. System-dependent values above are one recorded run.