C # traverse text box

#regiontext box Specify position add carriage return characterPrivate voidButton1_Click (Objectsender, EventArgs e) {            #region             //Query the first letter position//string str = "Ab0ab0ab0ab0"; //int one = str. IndexOf ("0"); //returns the position "index" where 0 appears//for (int i=0;i<str. length;i++)//{            //One = str. IndexOf ("0", ++one); //the second occurrence of the position//if (one==-1)//    {            //Break ;//not found//    }            //MessageBox.Show (one.            ToString ()); //}            #endregion            stringstr =TextBox1.Text.Trim (); intone = str. IndexOf ("</option>");//returns the position "index" where 0 appearsstr = str. Insert (one +9,"\ r \ n");  for(inti =0; I < Str. Length; i++) { One= str. IndexOf ("</option>", ++one);//the second occurrence of the position                if(One = =-1)                {                     Break;//not found                }                Else{str= str. Insert (one +9,"\ r \ n"); }} TextBox1.Text=str; }        #endregion        #regionList to string to remove text specified lineList<string> list =Newlist<string>(); Private voidButton2_Click (Objectsender, EventArgs e) {list.            Clear (); //            foreach(stringLineinchtextbox1.lines) {if(!line. Contains ("Select") ) {list.                ADD (line); }} TextBox1.Text=string. Join ("\ r \ n", List.        ToArray ()); }        #endregion

C # traverse text box