C#合并数组

C#合并数组
   private static char[] Str =   
      {   
        'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',   
        'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'   
      };
    private static char[] num =   
      {   
        '0','1','2','3','4','5','6','7','8','9'  
      };
    private static char[] spCharacter =   
      {   
        '~','!','#','@','$','%','^','&','*','(',')','-','_','=','+','\\',' ','[',']','{','}','|',';',':','"',',',   
        '<','.','>','/','?','`'  
      };
    public static string GenerateRandom(int Length, char[] sourceChar)
    {
        System.Text.StringBuilder newRandom = new System.Text.StringBuilder(52);
        Random rd = new Random();
        for (int i = 0; i < Length; i++)
        {
            newRandom.Append(sourceChar[rd.Next(sourceChar.Length)]);
        }
        return newRandom.ToString();
    }
    protected void btnGetStr_Click(object sender, EventArgs e)
    {
        if (!string.IsNullOrEmpty(txtLength.Text))
        {
            int Indx = ddlStr.SelectedIndex;
            char[] getStr = new char[] { };
            switch (Indx)
            {
                case 1:
                    getStr = num;
                    break;
                case 2:
                    getStr = Str;
                    break;
                case 3:
                    getStr = spCharacter;
                    break;
                case 4:
                    getStr = num.Union(Str).Distinct().ToArray();
                    break;
                case 5:
                    getStr = num.Union(spCharacter).Distinct().ToArray();
                    break;
                case 6:
                    getStr = Str.Union(spCharacter).Distinct().ToArray();
                    break;
                case 7:
                    getStr = Str.Union(spCharacter).Union(num).Distinct().ToArray();
                    break;
                default:
                    break;
            }
            int Length = Convert.ToInt32(txtLength.Text.ToString());
            this.txtStr.Text = GenerateRandom(Length, getStr);
            //this.lblLen.Text = this.txtStr.Text.ToString().Length.ToString();
        }