TopolearnEvery C# project, from a script to a web service, is created, built, tested and published through the same dotnet CLI.
C# code is compiled to IL (intermediate language) and run by the .NET runtime, which JIT-compiles it to machine code. You install the .NET SDK, which gives you the dotnet command.
dotnet new console -o Hellocreates a folder withHello.csproj(the project file) andProgram.cs.dotnet runbuilds and runs the project;dotnet buildonly compiles intobin/.dotnet test,dotnet add package <name>anddotnet publishcover testing, NuGet packages and deployment.
Since C# 9, a program can use top-level statements: you write code directly in Program.cs without a class Program and static void Main. The compiler generates the entry point for you, and args is available as a string[]. Only one file in a project may contain top-level statements.
.NET 10 adds file-based apps: dotnet run app.cs runs a single .cs file with no project at all, which is handy for scripts and experiments.
Console.WriteLine prints a line, Console.ReadLine reads one (it returns null at end of input, hence string?). The $"..." syntax is an interpolated string, covered in the strings lesson.
The project file sets the TargetFramework (for example net10.0) and options such as <Nullable>enable</Nullable> and <ImplicitUsings>enable</ImplicitUsings>, which pre-imports common namespaces like System and System.Linq.
Example
// Program.cs (create with: dotnet new console -o Hello; then: dotnet run)
// Top-level statements: no class or Main method needed.
Console.WriteLine("Hello, World!"); // Hello, World!
Console.WriteLine($"Args: {args.Length}"); // Args: 0
Console.Write("Your name? ");
string? name = Console.ReadLine(); // null if stdin is closed
Console.WriteLine($"Hi, {name ?? "stranger"}!");Remember
- The .NET SDK's dotnet CLI creates, builds, runs, tests and publishes projects
- Top-level statements replace the Main method boilerplate
- The .csproj file holds the target framework and compiler options
Watch out for
- Putting top-level statements in two files of the same project: only one entry point is allowed.