Why does a new project created using Visual Studio 2022 and the ASP.NET Core web app (Model, View, Controller) template not build?

I created a new project using Visual Studio 2022 and selected the template "ASP.NET Core Web App (Model-View-Controller)" but the project created won't build and I get the following error:

> Error CS5001
> Program does not contain a static 'Main' method suitable for an entry point

Program.cs

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddControllersWithViews();

var app = builder.Build();

// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Home/Error");
    // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
    app.UseHsts();
}

app.UseHttpsRedirection();
app.UseStaticFiles();

app.UseRouting();

app.UseAuthorization();

app.MapControllerRoute(
    name: "default",
    pattern: "{controller=Home}/{action=Index}/{id?}");

app.Run();

I tried removing the Program.cs file which did not fix it. I also tried creating a project from the "ASP.NET Core Web App" template which had the same issue.

You're using an old version of C#.

Reason

There's no class definition in your Program.cs, even though C# is object-oriented and all code must be inside classes.

Thus the compiler automatically generates a class called Program with a Main method inside, which takes an args argument of type string[]. Your code is put into that method. This concept is called top-level statements.

Top-level statements appeared in C# 9.0. If you're using an older version, the compiler will show an error message because it doesn't know how to handle code without class definition.

How to fix

Upgrade to C# 9 or higher. That's the solution.

If for some reasons you cannot do it, create a class and a Main method yourself:

using System;
// Using directives

namespace YourWebApp {
  public static class YourWebApp {
    public static void Main(string[] args) {
      // Your Program.cs code
    }
  }
}

> I tried removing the Program.cs file which did not fix it. I also
> tried creating a project from the "ASP.NET Core Web App" template
> which had the same issue.

Actually, while choosing a language version newer than the default can cause hard to diagnose compile-time and runtime errors. Most importantly, the latest C# compiler determines a default language version based on your project's target framework.

On top of this, Visual Studio doesn't provide a UI to change the value, but you can change it by editing the csproj file.

What causing the issue:

The issue you are having with this might occured due to numerous reasons.

First and foremost, when the framework and language version doen't match this may cause the issue. Each release of .NET runtime version has its compatible language version.

Let's have a look in following table:

Note: You can refer to this official document.

Check Runtime and Language Version Within Machine:

Another important point this that, check your .NET runtime within your machine. You can do that by following commands:

dotnet --list-sdks
dotnet --list-runtimes

Note: You can get more details here.

Check Runtime and Language Version Within Visual Studio:

Check what value do you have within your csproj file. You should get as following:

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>net7.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>

</Project>

Check Framework Version In Visual Studio:

Check Language Version In Visual Studio:

Note: I have .NET installed in my machine and Visual studio 2022 build version 17.5.2

Output:

If you create your MVC app following above steps let's say, using .NET6 and C# 10 you should get below program.cs file by default:

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddControllersWithViews();

var app = builder.Build();

// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Home/Error");
    // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
    app.UseHsts();
}

app.UseHttpsRedirection();
app.UseStaticFiles();

app.UseRouting();

app.UseAuthorization();

app.MapControllerRoute(
    name: "default",
    pattern: "{controller=Home}/{action=Index}/{id?}");

app.Run();

Note: Make sure, you have above configuration and setup according to the recommended way. If you still need further details you can refer to this official document.

Error CS5001 is mostly related to language version mismatch. C# 10.0 language version is available with .Net 6.0 base project. You can check that in Properties project => Build => Advanced

You can explicitly add <LangVersion>latest</LangVersion> or <LangVersion>10.0</LangVersion> in .csproj (project/web project) file

You can refer this doc https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/configure-language-version for more information.

I was able to determine that the cause of the error was illegal characters in the file path.

My project was in a parent folder that had been checked out from a TFS git repository. The TFS project had spaces in the name which on checkout were converted to %20. I was able to build and run the project after renaming the folder.

Original file path: My%20Git%20Repo/Projectname/
New file path: MyGitRepo/Projectname/