C# 如何生成验证码？

string str = "qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM1234567890";

Random ran = new Random();

int r = ran.Next(0, str.Length);

string a = str.Substring(r, 1);

用循环来选择验证码的位数：

string y = "";

Random ran = new Random();

for (int x = 1; x < 5; x++)

{

int r = ran.Next(0, str.Length);

string a = str.Substring(r, 1);

y = y + a;

}