Please select a valid startup item

I have migrated from Visual Studio 2008 to VS 2017.

I am getting this error when I try to run project with the green play button:

Obviously I have to select a valid startup item, but there are two pieces of information I need to do that:

1. what are typical valid startup items that I can try to select?

2. How do I select them?

I am a long time developer, but I am new to visual studio so please give me instructions based on terminology I can see on the screen.

It might be the case that you have opened your project using

File->Open->Folder

Use the right method to open your project using

File->Open->Project/Solution

or

File->Open->Website

File > New > Project From existing code. Select type of project > Next. Enter project name > Finish.

I went to File > Open > project/Solution and found the ".sln" file. I clicked on it and then pressed open and it worked for me. Just spent ages trying to figure this out!

Regards,

Open Visual Studio ------------------

1. Click File
2. Click Open
3. Open as Web Sites

Another method

1. Click File
2. Click Open
3. Open as Project

I found this question after I did File → Open → Folder as well. However in my case it's not a website, all I have is a source file. I don't want to create a full solution.

Now that Visual Studio supports CMake (to some degree), easiest is to add a simple CMakeLists.txt file, like this:

project (theproject)
add_executable (thetarget source.cpp)

As soon as the folder contains this file, Set as Startup Item turns up as a menu item in the Solution Explorer!

The only solution is that or this error:

> please select a valid startup file is that repair your visual studio

double click on visual studio installer and then click on the More then repair your visual studio