生成任意位数随机字符串

/// <summary> 
/// 产生随机字符串 
/// </summary> 
/// <param name="num">随机出几个字符</param> 
/// <returns>随机出的字符串</returns> 
private string GenCode(int num) 
{ 
string str = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"; 
//char[] chastr = str.ToCharArray(); //第二种
string code = ""; 
Random rd = new Random(); 
int i; 
for (i = 0; i < num; i++) 
{ 
//code += chastr[rd.Next(0, chastr.Length)]; //第二种
code += str.Substring(rd.Next(0, str.Length), 1); //第一种
} 
return code; 

}