C#

string str = "abcd1234";
for(int i = 0 ; i < str.Length ; i++)
if(str[i] < 58 && str[i]> 48)
{
....
}

using System;
using System.Windows.Forms;


public class test
{
	public test(){}
	
	public class nick : System.Windows.Forms.Form
	{
		public nick(){}
	}
	
	public static void Main(string[] args)
	{
		test t= new test();
		nick n = new nick();
		n.ShowDialog();
	}		
}

[StructLayout(LayoutKind.Sequential)]
public struct SHFILEINFO 
{
  public IntPtr hIcon;
  public IntPtr iIcon;
  public uint dwAttributes;
  [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]
  public string szDisplayName;
  [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 80)]
  public string szTypeName;
};
  

public const uint SHGFI_ICON = 0x100;
public const uint SHGFI_LARGEICON = 0x0;
public const uint SHGFI_SMALLICON = 0x1;

[DllImport("shell32.dll")]
public static extern IntPtr SHGetFileInfo(string pszPath,
                              uint dwFileAttributes,
                              ref SHFILEINFO psfi,
                              uint cbSizeFileInfo,
                              uint uFlags);

string file = @"C:\dir\blah.doc";
IntPtr hImg = SHGetFileInfo(file , 0, ref shinfo,
                                  (uint)Marshal.SizeOf(shinfo),
                                   Win32.SHGFI_ICON |
                                   Win32.SHGFI_SMALLICON);
Icon i = Icon.FromHandle(hImg);