帮我看一下这段代码，，红色部分是错误的


using System;
using System.Collections.Generic;
using
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using MySchoolDAL;
using MySchoolmodel;

namespace MySchool
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void BTAddStudent_Click(object sender, EventArgs e)
        {
            Student student = new Student();
            student.StudentNo = Convert.ToInt32(this.txtStudentNo.Text.Trim());
            student.LoginPwd = this.txtLoginPwd.Text.Trim();
            student.StudentName = this.txtStudentName.Text.Trim();
            string Grender = null;
            if(this.RBF.Checked==true)
                {
                   Gender=this.RBF.Text;
           
                }
             if(this.RBS.Checked==true)
                {
                    Gender=this.RBS.Text;
                 }

                student.Gender =Gender ;
                 student .GradeID=this.CBGradeID.SelectedItem.ToString ();
                 if(StudentServices1.AddStudent(student)>0)
                 {
                     MessageBox .Show("添加学生信息成功！");
                 }
                 else
                 {
                     return ;
                 }
 

        }

      
     

      
    }
}

Gender=this.RBF.Text.tostring();//this.RBF.Text.tostring()要有数据，要不然要先进行判断   student.Gender =Gender 一样也要.tostring()

[ 本帖最后由 sbadwaps 于 2013-10-18 21:46 编辑 ]

string Grender = "";
字符串初始化的时候不要给null。这样的习惯很不好。