关于制作中的学生管理系统的问题,请高手进来看看,帮帮忙,网上找不到语句...本人很菜,没学过

这是整个程序,想达到的目的很简单,就是可以实施简单的添加修改查找和删除的行为
修改还不知道如何着手,已经出现问题...
由于没有书,删除和查找语句都是网上找来的
没有学过.NET语言,真不知道怎么改
错误就是用红色字标出的地方
哥哥姐姐快帮帮我吧
程序在下面
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;using System.Data.SqlClient;
using MyForm.DBLibrary;
using MyForm.Common;namespace MyForm
{
    public partial class frmStudent : Form
    {
        DBBase dbBase = new DBBase();
        DataSet ds = new DataSet();
        DataTable dt = new DataTable();
        Utility utility;
        
        public frmStudent()
        {
            InitializeComponent();
        }        private void LoadStudent()
        {
            String sql = "select * from students";
            dt = dbBase.ExecuteSQLGetDataTable( sql );
            dgvStudent.DataSource = dt;           
        }
        private void LoadDep()
        {
            String sqlText = "select * from Department";
            dt = dbBase.ExecuteSQLGetDataTable(sqlText);
           
            cmbSdept.DataSource = dt;
            cmbSdept.DisplayMember = "Sdept";
            //cmbDep.r
        }
        private void frmStudent_Load(object sender, EventArgs e)
        {
            LoadStudent();
            LoadDep();
            utility = new Utility(this);
            utility.SetControlsEnable(false);
            SetButtonStatus(false);        }        private void dgvStudent_CellContentClick(object sender, DataGridViewCellEventArgs e)
        {
            DataGridViewRow row = dgvStudent.Rows[e.RowIndex];
            String ID = row.Cells["colSno"].Value.ToString().Trim();
            String name = row.Cells["colName"].Value.ToString().Trim();
            if (e.ColumnIndex == row.Cells["coldetail"].ColumnIndex)
            {                frmStudentDetail frm = new frmStudentDetail(name, ID);
                frm.Owner = this;
                frm.ShowDialog();
            }
           
        }        private void dgvStudent_KeyDown(object sender, KeyEventArgs e)
        {
            
            if (e.KeyData == Keys.Enter)
            {
                String ID = dgvStudent.Rows[dgvStudent.CurrentCellAddress.Y].Cells["colSno"].Value.ToString().Trim();
                //String ID = row.Cells["colSno"].Value.ToString().Trim();dgvStudent.Rows[dgvStudent.CurrentCellAddress.Y].Cells["colName"].Value.ToString().Trim()
                String name = dgvStudent.Rows[dgvStudent.CurrentCellAddress.Y].Cells["colName"].Value.ToString().Trim();
                frmStudentDetail frm = new frmStudentDetail(name, ID);
                frm.Owner = this;
                frm.ShowDialog();            }
             
        }        private void btnClose_Click(object sender, EventArgs e)
        {
            this.Close();
            Dispose(true);
        }
        private void SetButtonStatus(bool flag)
        {
            btnAdd.Visible = !flag;
            btnSave.Visible = flag;
            btnCancel.Visible = flag;        }        private void btnAdd_Click(object sender, EventArgs e)
        {
            utility.SetControlsEnable(true);
            SetButtonStatus(true);
            utility.ClearContent();
        }        private void btnSave_Click(object sender, EventArgs e)
        {
            if (!utility.CheckNull())
                return;
            //
            String strSno = tbSno.Text.Trim();
            String strName = tbSname.Text.Trim();
            String strSex = cmbSsex.Text.Trim();
            String strAge = tbSage.Text.Trim();
            String strDept = cmbSdept.Text.Trim();            String sqlText = "insert into students(Sno,Sname,Ssex,Sage,Sdept) values('" + strSno + "','"
                                                                                        + strName + "','"
                                                                                        + strSex + "','"
                                                                                        + strAge + "','"
                                                                                        + strDept + "')";
            bool tag = dbBase.ExecuteSQL(sqlText);
            if (tag)
            {
                MessageBox.Show("插入成功！");
            }
            LoadStudent();
            utility.SetControlsEnable(false);
            SetButtonStatus(false);
            utility.ClearContent();
            
            dgvStudent.Rows[0].Selected = false;
            foreach (DataGridViewRow row in dgvStudent.Rows)
            {
                if (row.Cells["colSno"].Value.ToString().Trim() == strSno)
                {
                    row.Selected = true;
                }
                 
            }
            
        }        private void btnCancel_Click(object sender, EventArgs e)
        {
            SetButtonStatus(false);
            utility.SetControlsEnable(false);
            utility.ClearContent();
        }        private void tbSage_Validating(object sender, CancelEventArgs e)
        {        }        private void btselect_Click(object sender, EventArgs e)
        {
           SqlCommand mySqlCommand=new SqlCommand("GetSno",myConnection); 
           mySqlCommand.CommandType=CommandType.StoredProcedure;
        }
        private void btdelete_Click(object sender, EventArgs e)
        {
            String strSno = tbSno.Text.Trim();
            ds.Clear();
            string deleteString = "delete   from   students   where   sno='" + strSno + "'";
            SqlCommand mySqlCommand = new SqlCommand(); 
            mySqlCommand.CommandText = deleteString;
            mySqlCommand.ExecuteNonQuery();   
 
        }
    }
}