C# Online Compiler | Free Online Compiler

Code

using System;

class Program {
    static void Main(string[] args) {
        Console.WriteLine("Hello, C#!");
        if (args.Length > 0) {
            Console.WriteLine("First arg: " + args[0]);
        }
    }
}

STDIN (optional)

Args (space separated)

Output

What Is the C# Online Compiler?

This tool lets you compile and run C# console programs directly in your browser without installing Visual Studio, the .NET SDK, or any other tooling on your machine. Whether you are learning C# for the first time or quickly testing language features like LINQ, async/await, or generics, this compiler provides a fast way to write and execute C# code online.

Your code must include a static void Main(string[] args) entry point inside a class, which is the standard starting method for C# console applications. You can use Console.WriteLine to print output, read input with Console.ReadLine, and work with the full range of .NET base class library types.

All code executes on a remote sandboxed server powered by the Piston API. Your browser sends the source code to the server, which compiles it using the .NET/Mono runtime and runs the resulting program inside an isolated container. C# type checking, null reference checks, and other compiler diagnostics are fully enforced during compilation.

How It Works

Write your C# code in the editor panel. The editor starts with a simple "Hello, C#!" example using Console.WriteLine, but you can replace it with any valid C# console program.
Provide input in the STDIN field if your program reads from standard input using Console.ReadLine(). Leave this field empty if your program does not require input.
Add command-line arguments in the Args field if your program reads from the args parameter in Main. Enter arguments separated by spaces.
Click the Run button to send your code to the Piston execution server. The server compiles your C# source code and then executes the resulting program, capturing all output.
View the results in the Output panel. You will see everything your program prints to standard output, along with any compiler errors including type mismatches, missing references, or runtime exceptions.

Step-by-Step Example

Suppose you want to write a program that reads a list of numbers from standard input and uses LINQ to compute the sum and average. Here is how you would do it using this compiler:

First, type the following code into the editor panel:

using System;
using System.Linq;

class Program {
    static void Main(string[] args) {
        Console.Write("Enter numbers separated by spaces: ");
        string input = Console.ReadLine();

        int[] numbers = input.Split(' ')
            .Select(int.Parse)
            .ToArray();

        Console.WriteLine($"Sum: {numbers.Sum()}");
        Console.WriteLine($"Average: {numbers.Average():F2}");
        Console.WriteLine($"Count: {numbers.Length}");
    }
}

This example demonstrates several C# features: using directives for namespace imports, LINQ methods like Select, Sum, and Average, string interpolation with $"", and array operations.

Next, go to the STDIN field and type some numbers, for example 10 20 30 40 50. These values will be read by Console.ReadLine when the program runs.

Now click the Run button. The compiler first builds your C# source code, then executes it with the provided input. After a moment, the Output panel displays the result:

Enter numbers separated by spaces: Sum: 150
Average: 30.00
Count: 5

You can modify the STDIN values and click Run again to test with different input. This workflow makes it easy to experiment with LINQ queries and other C# features interactively.

Use Cases

Learning C# fundamentals. Beginners can experiment with variables, data types, control flow, classes, interfaces, and inheritance in a zero-setup environment.
Testing LINQ queries. Quickly verify how LINQ methods like Where, Select, GroupBy, and Aggregate transform collections without setting up a project.
Practicing algorithms and data structures. Implement sorting algorithms, tree traversals, and other common problems using C# collections like List<T>, Dictionary<K,V>, and Queue<T>.
Exploring async/await patterns. Experiment with Task-based asynchronous programming and understand how async and await keywords work in console applications.
Preparing for coding interviews. Many interview questions can be solved in C#. Use this compiler to practice problems, test edge cases, and refine solutions quickly.

Limitations and Notes

Single file execution only. This compiler runs a single C# file (Program.cs). Multi-file projects with separate class files are not supported.
No NuGet packages. The NuGet package manager is not available. You cannot import external libraries beyond the .NET base class library.
Console applications only. GUI frameworks like Windows Forms, WPF, and MAUI are not supported. Only console output and input are available.
No project or solution files. There is no support for .csproj or .sln files. All code must be self-contained in a single file.
No file I/O access. The sandboxed environment does not allow reading from or writing to the filesystem. File operations will fail at runtime.
Execution timeout applies. Programs that take too long or enter infinite loops are terminated automatically to prevent resource exhaustion.
Base class library is available. You can use namespaces like System, System.Linq, System.Collections.Generic, System.Text, and other standard library features.

Frequently Asked Questions

What C# version does this compiler use?

It uses the C# version available through the .NET/Mono runtime provided by the Piston execution engine.

Can I use Console.ReadLine for input?

Yes, use Console.ReadLine() in your code and provide the input data in the STDIN field before running.

Does this compiler support LINQ?

Yes, LINQ is fully supported. You can use System.Linq with query expressions and method syntax.

Can I install NuGet packages?

No, NuGet package management is not available. Only the standard .NET base class library is accessible.

Does async/await work?

Yes, you can use async and await keywords along with Task-based asynchronous patterns in your console programs.

Can I define multiple classes?

Yes, you can define multiple classes within a single file. All classes must be in the same source file.

Can I build Windows Forms or WPF apps?

No, this compiler supports console applications only. GUI frameworks like Windows Forms and WPF are not available.

Is there a compilation step?

Yes, your C# code is compiled before execution. You will see compiler errors for syntax issues, type mismatches, and missing references.

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