I just started learning c#, I created C# console application. To understand the concepts, I watched videos of how to setup vs code for c#
When I run the dotnet new console command in VS code terminal, it creates a new project including Program.cs file.
In the video, the Program.cs file appears like that
// Program.cs
using System;
namespace HelloWorld
{
class Program
{
static string Main(string[] args)
{
Console.WriteLine("Hello, World!");
}
}
}
Program.cs in my IDE appears like,
// Program.cs
// See https://aka.ms/new-console-template for more information
Console.WriteLine("Hello, World!");
When I run the code using terminal dotnet run it runs perfectly on my computer.
when I create a new cs file, it contains
// hello.cs
Console.WriteLine("hello world");
after running it says Only one compilation unit can have top-level statements.
when I use class method and namespace like
// hello.cs
namespace helloworld
{
class hello
{
static void Main()
{
Console.WriteLine("hello world");
}
}
}
it runs THE Program.cs file not the new file and shows this warning
PS C:\Users\User\C#projects> dotnet run hello.cs C:\Users\User\C#projects\hello.cs(5,21): warning CS7022: The entry point of the program is global code; ignoring 'hello.Main()' entry point. [C:\Users\User\C#projects\C#projects.csproj] Hello, World!
Project structure:
I tried another method by pressing run and debug and show nothing.
When I click on Generate c# Assets for Build and Debug button it shows this
Could not locate .NET Core project. Assets were not generated.
CodePudding user response：
C# 9 feature: Top-level statements
This is a newly introduced feature in C# 9 called Top-level statements
The video to which you are referring might be using a lower version of C#(lower than C# 9). Where we use to get
namespace helloworld
{
class hello
{
static void Main()
{
Console.WriteLine("hello world");
}
}
}
as a default structure of Main program.
If you look closely you will find, only one line of code which prints a string to the console i.e.
Console.WriteLine("hello world");
Top-level statements were introduced to remove unnecessary ceremony from this console application.
As you are using C#9 or higher, dot net run with top-level statement compiling your code successfully, but when you are replacing one-liner code to legacy structure, then compiler warns you regarding the global entry of Main function and Main() function which you added by replacing top-level statement.
To Get more clarity you can go through MSDN documentation: Top-level statements
Why you are getting an error "Only one compilation unit can have top-level statements."?
- As per the MSDN documentation, An application must have only one entry point.
- A project can have only one file with top-level statements.
- When you created a new file, you added a new top-level statement which result in below compile time error:
CS8802 Only one compilation unit can have top-level statements.
how to fix it?
- As per the above explanation, your project should not contain two or more top-level statements. To fix this error, you can delete a file that was added later on.
CodePudding user response：
In C# 9 You can use top level statement in only one file please refer to the docs