public string str_userName;        //用户名(登陆传过来的)

        public string str_SIM;

        public string str_name;        //姓名(查询页面穿过来的)

        public string str_sex;         //性别(查询页面穿过来的)

        public Frm_StudentInfoManagement(string str)        //按用户名重载
        {
            str_userName = str;

            InitializeComponent();
        }

        public Frm_StudentInfoManagement(int intNO)     //按学号重载
        {
            int_studentsNumber = intNO;

            InitializeComponent();
        }

        public Frm_StudentInfoManagement(string strName,string strSex)        //按姓名,性别重载
        {
            str_name = strName;

            str_sex= strSex;

            InitializeComponent();
        }

private void SIM_select()     //学生信息查询条件
        {
            if (int_studentsNumber == 0)       //没有传过来学号
            {
                if (str_name == "" && str_sex == "")        //姓名,性别为空
                {
                    str_SIM = "1";
                }
                else if (str_name != "" && str_sex == "")     //姓名不为空&&性别为空
                {
                    str_SIM = "2";
                }
                else if (str_name != "" && str_sex != "")        //姓名不为空&&性别不为空
                {
                    str_SIM = "3";
                }
            }
            else
            {
                str_SIM = "4";
            }
        }

得到的值为什么是3

[[it] 本帖最后由 sun_life 于 2008-11-13 10:34 编辑 [/it]]

生能帮忙看看阿？

晕，这个问题需要问？页面传来值姓名跟性别了
&&相当于and的意思
2个都不为空，则为 str_SIM = "3";

你传的什么过来？构造函数有3个，你不给个测试数据，谁知道调用哪个构造函数啊？

调试一下啊 看看是否传来数据

你写的业务逻辑是这样的， 除非这两个变量是这样赋值的 str_name = "";str_sex = "";  才不可能触发第三个if  

记住空对象[null] 不等于 [""] 空字符