ParameterDirection.ReturnValue用法

SqlCommand mycom = usercommon.createcommand();
mycom.CommandText = "ModifyUserPwd";
SqlParameter[] parm ={ new SqlParameter("@username", SqlDbType.VarChar, 50), new SqlParameter("@userpwd", SqlDbType.VarChar, 50), new SqlParameter("@newpwd", SqlDbType.VarChar, 50),new SqlParameter("@returnvalue",SqlDbType.Int) };
parm[0].Value=username;
parm[1].Value=oldpwd;
parm[2].Value=newpwd;
parm[3].Direction = ParameterDirection.ReturnValue;
usercommon.AttachParameters(mycom,parm);
mycom.ExecuteNonQuery();
int i =(Int32) mycom.Parameters["@returnvalue"].Value;
usercommon.CloseConn();
return i;

alter proc ModifyUserPwd
(
@username varchar(50),
@userpwd varchar(50),
@newpwd varchar(50)
)
as
declare @pwd varchar(50)
select @pwd=userpwd from users
if(@pwd=@userpwd)
begin
update users set userpwd=@newpwd where username=@username
return 1
end
else
return 0
go