How to run a program (C#)

How to: Run a C# program in Visual Studio

10/16/2019

6 minutes to read

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In this article

What you need to do to run a program depends on what you're starting from, what type of program, app, or service it is, and whether you want to run it under the debugger or not. In the simplest case, when you have a project open in Visual Studio, build and run it by pressing

Ctrl

+

F5

(

Start without debugging

) or

F5

(

Start with debugging

), or press the green arrow (

Start Button

) on the main Visual Studio toolbar.

Starting from a project

If you have a C# project (

.csproj

file), then you can run it, if it is a runnable program. If a project contains a C# file with a

Main

method, and its output is an executable (EXE), then most likely it will run if it builds successfully.

If you already have the code for your program in a project in Visual Studio, open the project. To open the project, double-click or tap on the

.csproj

from the Windows File Explorer, or from Visual Studio, choose

Open a project

, browse to find the project (

.csproj

) file, and choose the project file.

After the projects loads in Visual Studio, press

Ctrl

+

F5

(

Start without debugging

) or use the green

Start

button on the Visual Studio toolbar to run the program. If there are multiple projects, the one with the

Main

method must be set as the startup project. To set the startup project, right-click on a project node, and choose

Set as startup project

.

Visual Studio attempts to build and run your project. If there are build errors, you see the build output in the

Output

window and the errors in the

Error List

window.

If the build succeeds, the app runs in a way that's appropriate for the type of project. Console apps run in a terminal window, Windows desktop apps start in a new window, web apps start in the browser (hosted by IIS Express), and so on.

Starting from code

If you're starting from a code listing, code file, or a small number of files, first make sure the code you want to run is from a trusted source and is a runnable program. If it has a

Main

method, it is likely intended as a runnable program that you can use the Console App template to create a project to work with it in Visual Studio.

Code listing for a single file

Start Visual Studio, open an empty C# console project, select all the code in the .cs file that's in the project already, and delete it. Then, paste the contents of your code into the .cs file. When you paste the code, overwrite or delete the code that was there before. Rename the file to match the original code.

Code listings for a few files

Start Visual Studio, open an empty C# console project, select all the code in the .cs file that's in the project already, and delete it. Then, paste the contents of the first code file into the .cs file. Rename the file to match the original code.

For a second file, right-click on the project node in

Solution Explorer

to open the shortcut menu for the project, and choose

Add > Existing Item

(or use the key combination

Shift

+

Alt

+

A

), and select the code files.

Multiple files on disk

Create a new project of the appropriate type (use C#

Console App

if you're not sure).

Right-click on the project node, se

Add

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>

Existing Item

to select the files and import them into your project.

Starting from a folder

When you're working with a folder of many files, first see if there's a project or solution. If the program was created with

.csproj

extension or .sln extension and in the Windows File Explorer, double-click on one of them to open them in Visual Studio. See

Starting from a Visual Studio solution or project

.

If you don't have a project file, such as if the code was developed in another development environment, then open the top-level folder by using the

Open folder

method in Visual Studio. See

Develop code without projects or solutions

.

Starting from a GitHub or Azure DevOps repo

If the code you want to run is in GitHub or in an Azure DevOps repo, you can use Visual Studio to open the project directly from the repo. See

Open a project from a repo

.

Run the program

To start the program, press the green arrow (

Start

button) on the main Visual Studio toolbar, or press

F5

or

Ctrl

+

F5

to run the program. When you use the

Start

button, it runs under the debugger. Visual Studio attempts to build the code in your project and run it. If that succeeds, great! But if not, continue reading for some ideas on how to get it to build successfully.

Troubleshooting

Your code might have errors, but if the code is correct, but just depends on some other assemblies or NuGet packages, or was written to target a different version of .NET, you might be able to easily fix it.

Add references

To build properly, the code must be correct and have the right references set up to libraries or other dependencies. You can look at the red squiggly lines and at the

Error List

to see if the program has any errors, even before you compile and run it. If you're seeing errors related to unresolved names, you probably need to add a reference or a using directive, or both. If the code references any assemblies or NuGet packages, you need to add those references in the project.

Visual Studio tries to help you identify missing references. When a name is unresolved, a light bulb icon appears in the editor. If you click the light bulb, you can see some suggestions on how to fix the issue. Fixes might be to:

add a using directive

add a reference to an assembly, or

install a NuGet package.

Missing using directive

For example, in the following screen, you can choose to add

using System;

to the start of the code file to resolve the unresolved name

Console

:

Missing assembly reference

.NET references can be in the form of assemblies or NuGet packages. Usually, if you find source code, the publisher or author will explain what assemblies are required and what packages the code depends on. To add a reference to a project manually, right-click on the

References

node in the

Solution Explorer

, choose

Add Reference

, and locate the required assembly.

You can find assemblies and add references by following the instructions in

Add or remove references by using the reference manager

.

Missing NuGet package

If Visual Studio detects a missing NuGet package, a light bulb appears and gives you the option to install it:

If that doesn't solve the issue and Visual Studio can't locate the package, try searching for it online. See

Install and use a NuGet package in Visual Studio

.

Use the right version of .NET

Because different versions of the .NET Framework have some degree of backward compatibility, a newer framework might run code written for an older framework without any modifications. But, sometimes you need to target a specific framework. You might need to install a specific version of the .NET Framework or .NET Core, if it's not already installed. See

Modify Visual Studio

.

To change the target framework, see

Change the target framework

. For more information, see

Troubleshooting .NET Framework targeting errors

.

Next steps

Explore the Visual Studio development environment by reading

Welcome to the Visual Studio IDE

.

See also