SqlParameter怎么不能带单引号

C# code

//参数sql语句写法                //SqlParameter[] paras =                //{new SqlParameter("@username",SqlDbType.NVarChar),                // new SqlParameter("@ip",SqlDbType.NVarChar),                // new SqlParameter("@time",SqlDbType.DateTime),                // new SqlParameter("@logstate",SqlDbType.Bit),                // new SqlParameter ("@illegal",SqlDbType.Bit),                //};                //paras[0].Value = username;                //paras[1].Value = ip;                //paras[2].Value = time;                //paras[3].Value = logstate;                //paras[4].Value = illegal;                //string sqlcmd = "insert into User_Log (用户名,ip,登陆时间,在线状态,非法登陆) values "+"(" +@username + "," +@ip+ "," +@time+ "," +@logstate+ "," +@illegal+")" ;                                SqlCommand cmd = new SqlCommand(sqlcmd, conn);                                //cmd.Parameters.Add(paras[0]);                //cmd.Parameters.Add(paras[1]);                //cmd.Parameters.Add(paras[2]);                //cmd.Parameters.Add(paras[3]);                //cmd.Parameters.Add(paras[4]);

哪里写错了吗？sqlcmd的写法对不对。
另外，如果我用：

C# code

//foreach (SqlParameter i in paras)                //{                //    cmd.Parameters.Add(paras);                //}

就要报错，该怎么写

[解决办法]

C# code

string sqlcmd = "insert into User_Log (用户名,ip,登陆时间,在线状态,非法登陆) values(@username,@ip,@time,@logstate,@illegal)" ;
[解决办法]
C# code
//参数sql语句写法                SqlParameter[] paras =                {new SqlParameter("@username",SqlDbType.NVarChar),                 new SqlParameter("@ip",SqlDbType.NVarChar),                 new SqlParameter("@time",SqlDbType.DateTime),                 new SqlParameter("@logstate",SqlDbType.Bit),                 new SqlParameter ("@illegal",SqlDbType.Bit),                };                paras[0].Value = username;                paras[1].Value = ip;                paras[2].Value = time;                paras[3].Value = logstate;                paras[4].Value = illegal;                string sqlcmd = "insert into User_Log (用户名,ip,登陆时间,在线状态,非法登陆) values (@username,@ip,@time,@logstate,@illegal)" ;                                SqlCommand cmd = new SqlCommand(sqlcmd, conn);                               cmd.Parameters.AddRange(paras);