how to get full path from filename in c# code example

Example 1: c# get folder of full ilepath

string fileName = @"test.txt";
    string currentDirectory = Directory.GetCurrentDirectory();
    string[] fullFilePath = Directory.GetFiles(currentDirectory, filename, SearchOption.AllDirectories);

Example 2: c# how to get a file path from user

OpenFileDialog choofdlog = new OpenFileDialog();
choofdlog.Filter = "All Files (*.*)|*.*";
choofdlog.FilterIndex = 1;
choofdlog.Multiselect = true;

if (choofdlog.ShowDialog() == DialogResult.OK)    
{     
    string sFileName = choofdlog.FileName; 
    string[] arrAllFiles = choofdlog.FileNames; //used when Multiselect = true           
}