Prüfen ob
IsAlphaNumericString: ein String eine gültige Zahl ist
IsNumeric: ein gültiger Alpha-numerischer String ist

public bool IsAlphaNumericString(string strAlphanum) { System.Text.RegularExpressions.Regex pattern = new System.Text.RegularExpressions.Regex( @"^[A-Za-z0-9]+$" ); return pattern.IsMatch(strAlphanum.Trim()); }<br /> public bool IsNumeric(string strAlphanum) { System.Text.RegularExpressions.Regex pattern = new System.Text.RegularExpressions.Regex( @"^[0-9]+$" ); return pattern.IsMatch(strAlphanum.Trim()); }

To generate a square thumbnail in c#, use this code:
public Bitmap Generate75x75Pixel(Bitmap image) { if(image == null)     throw new ArgumentNullException("image");     Bitmap bmp = null;     Bitmap crapped = null;     int x = 0, y = 0;     double prop = 0;     if(image.Width > 75) {         // compute proportation         prop = (double)image.Width / (double)image.Height;         if(image.Width > image.Height) {             x = (int)Math.Round(75 * prop, 0);             y = 75;         }         else {             x = 75;             y = (int)Math.Round(75 / prop, 0);         }         bmp = new Bitmap((Image)image, new Size(x, y));         crapped = new Bitmap(75, 75);         Graphics g = Graphics.FromImage(crapped);         g.DrawImage(bmp,             new Rectangle(0, 0, 75, 75),             new Rectangle(0, 0, 75, 75),             GraphicsUnit.Pixel         );         bmp = crapped; } else { crapped = image; } return bmp; }