//IsRegUserOk函数：判断用户是否已经注册和密码是否正确
public bool IsRegUserOk()
{
string name=TextBoxName.Text.Trim();
string pwd=TextBoxPassword.Text.Trim();
//建立/打开数据库连接
SqlConnection conn=new SqlConnection();
conn.ConnectionString="server=(local);uid=sa;pwd=;database=jxdb";
conn.Open();
//建立sql字符串
string sql="select * from reg where name='"+name+"'";
SqlDataReader dr;
SqlCommand cmd=new SqlCommand(sql,conn);
dr=cmd.ExecuteReader();
//保留用户注册与否信息
bool isRegUserExist=dr.Read();
//关闭DataReader
dr.Close();
//取得用户名的密码
string sqlBoth="select * from reg where name='"+name+"'";
sqlBoth+="and pwd='"+pwd+"'";
SqlCommand cmdBoth=new SqlCommand(sqlBoth,conn);
SqlDataReader drBoth;
drBoth=cmdBoth.ExecuteReader();
//保留用户名+密码同时存在信息
bool isBothExist=drBoth.Read();
//关闭DataReader
drBoth.Close();
conn.Close();
//判断用户是否注册

(编辑:aniston)