字母，数字，正则

//生成数字加字母的字符串的方法
    public static string ToRandPwd()
    {
        Random random = new Random();
        int pwdLength = random.Next(6, 10);//密码长度控制在6到10位之间
        string password = "";
        string temp1 = string.Empty;
        int digitNum1 = random.Next(pwdLength - 1);
        if (digitNum1 == 0)
        {
            digitNum1 = 1;
        }
        int charUpperNum1 = random.Next(pwdLength - digitNum1);
        if (charUpperNum1 == 0)
            charUpperNum1 = 1;
        int charLowerNum1 = pwdLength - digitNum1 - charUpperNum1;

        for (int i = 0; i < digitNum1; i++)
        {
            temp1 += random.Next(0, 10);//digit
        }
        for (int i = 0; i < charUpperNum1; i++)
        {
            temp1 += (char)random.Next(65, 91);//upper case
        }
        for (int i = 0; i < charLowerNum1; i++)
        {
            temp1 += (char)random.Next(97, 123);
        }

        for (int i = 0; i < pwdLength; i++) //disarrange password
        {
            int n = random.Next(temp1.Length);
            password += temp1[n];
            temp1 = temp1.Remove(n, 1);
        }

        return password;
    }

using System.Text.RegularExpressions;

if(Regex.IsMatch(this.TextBox1.Text,@"^(?!([^A-Za-z]|\d)+$)[a-zA-Z\d]{6,}$")) //@"^(?!\D+$)(?![^a-z]+$)[a-zA-Z\d]{6,}$"
        {
            Response.Write("你输入的符合是至少为六位且必须是数字和字母组合的字符串");
        }

if (Regex.IsMatch(this.TextBox1.Text, @"^[A-Za-z]+$"))
        {
            Response.Write("都是字母");
        }