Check if a folder exist in a directory and create them using C#

This should help:

using System.IO;
...

string path = @"C:\MP_Upload";
if(!Directory.Exists(path))
{
    Directory.CreateDirectory(path);
}

using System.IO;
...

Directory.CreateDirectory(@"C:\MP_Upload");

Directory.CreateDirectory does exactly what you want: It creates the directory if it does not exist yet. There's no need to do an explicit check first.

Any and all directories specified in path are created, unless they already exist or unless some part of path is invalid. The path parameter specifies a directory path, not a file path. If the directory already exists, this method does nothing.

(This also means that all directories along the path are created if needed: CreateDirectory(@"C:\a\b\c\d") suffices, even if C:\a does not exist yet.)

---

Let me add a word of caution about your choice of directory, though: Creating a folder directly below the system partition root C:\ is frowned upon. Consider letting the user choose a folder or creating a folder in %APPDATA% or %LOCALAPPDATA% instead (use Environment.GetFolderPath for that). The MSDN page of the Environment.SpecialFolder enumeration contains a list of special operating system folders and their purposes.

if(!System.IO.Directory.Exists(@"c:\mp_upload"))
{
     System.IO.Directory.CreateDirectory(@"c:\mp_upload");
}