How to find if a file is an exe?

Question

How can I be sure that a file passed to my program is a valid exe file ?

actually my program takes a file as input and runs it, but user can input any file so I have

Answer 1

If you want to just check the file extension:

if (String.Equals(Path.GetExtension(filePath), ".exe", StringComparison.InvariantCultureIgnoreCase))
{
    ...
}

If you need to verify that the file is really executable you can analyze its header. There is information about .exe file header: link.

You also can try to run the file as 0xA3 suggested