using System;
using System.Data.OleDb;


namespace WindowsFormsApplication1
{
    class DB
    {
        public static bool logo(string g, string n, string pwd)
        {
            String strconnection = "Provider=Microsoft.Jet.OleDb.4.0；";//Data source = |DataDirectory| \\info.mdb:";
            strconnection += @"Data Source=|DataDirectory|\info.mdb";
            OleDbConnection cn = new OleDbConnection(strconnection);
            cn.Open();
            OleDbCommand command = new OleDbCommand();
            try
            {
                string sql = "select count(*) from userInfo where(group='" + g + "'and username='" + n + "'and password='" + pwd + "')";
            }catch(Exception){
               
            
            }

                int num = 0;
                num = (int)command.ExecuteScalar();
                cn.Close();
                if (num == 1)
                    return true;
                else
                    return false;
        
               
            }
        }
    }

num=int.Parse(command.ExecuteScalar().Tostring());
我这是这么写的，你自己的有没有错我也没试过。

OleDbCommand command = new OleDbCommand();
try
{
      string sql = "select count(*) from userInfo where(group='" + g + "'and username='" + n + "'and password='" + pwd + "')";
 }catch(Exception){
               
            
}
= CommandType.Text;
= sql;

有没有错误 你编译一下不就知道了 别什么都问 至少在自己动手之后

最起码大括号少了几个，还是自己先试过了再问吧，这样达人们也会比较愿意帮忙。

在VS里面编译一下就会知道有没有错了