包含casevb.net的詞條
VB中的CASE語句
在VB.NET中VB.NET CASE語句就是比較常用的一種，下面是詳細(xì)的介紹和代碼的演示：
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1、可以用 Select...Case 語句來替換 If...Then...Else 語句，所不同的是If 和 ElseIf 語句可在每個語句中計算不同的表達(dá)式，而 Select 語句對單個表達(dá)式只計算一次，然后將其和不同的值比較。
Function?bonus(ByVal?performance?As?Integer,?_??ByVal?salary?As?Decimal)?As?Decimal??
Select?performance??
Case?1??
Return?salary?*?0.1??
Case?2??
Return?salary?*?0.3??
Case?3??
Return?salary?*?0.7??
Case?4??
Return?salary?*?0.9??
Case?5??
Return?salary?*?1.2??
End?Select??
End?Function
2、VB.NET Case語句可包含多個值和某個范圍的值，代碼案例如下：
Function?bonus(ByVal?performance?As?Integer,?_??ByVal?salary?As?Decimal)?As?Decimal??
Select?performance??
Case?1??
Return?salary?*?0.1??
Case?2,3??
Return?salary?*?0.3??
Case?3?To?7??
Return?salary?*?0.7??
Case?8?To?9??
Return?salary?*?0.9??
Case?Is?=?15??
Return?salary?*?1.2??
Case?Else??
Return?0??
End?Select??
End?Function
在VB.net中，使用Select Case語句，Case后能接幾個判斷語句嗎？
select case when a1 and b2 and c3 then d=1
when a1 and b2 and c3 then d=2
... end
至于寫多少，沒限制，，只要你語句不卡，，，
求做一個web頁面控制服務(wù)器串口，可用Mscomm控件做！滿意會繼續(xù)最佳。htm頁面都能操作本地串口。
看了你的留言直接在這回吧，其實網(wǎng)頁方面我也是個菜鳥。去年我做過一個類似的，當(dāng)時也是自學(xué)了1個月的iis的配置，asp.net，vb串口操作等，大二假期比較閑。
做法：用DS18B20溫度傳感器連接51單片機，然后單片機通過串口與電腦通信，電腦成為服務(wù)器，手機連接網(wǎng)頁，進(jìn)行溫度監(jiān)控，開關(guān)單片機外接的繼電器等等操作。
硬件端的代碼對你沒用，服務(wù)器端我的基本思路就是asp.net連接數(shù)據(jù)庫，然后用vb實時掃描數(shù)據(jù)庫，通過vb中的MScomm控件連接串口，vb的代碼對你也沒啥用，因為MScomm連接單片機的代碼的“通信協(xié)議”我是寫在單片機上的，不配套就沒用了
這是網(wǎng)頁的代碼，不精簡，高手莫笑...
主要功能就是連接數(shù)據(jù)庫。。。里面沒能直接通過asp.net控制串口，貌似也有C#直接控制的，你去CSDN看看吧，我試過是沒問題的，就是操作不太方便（可能我太菜了）
using System;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.SqlClient;
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
//溫度
SqlConnection cnn1 = new SqlConnection(@"Data Source=YINGJHSHP541\SQLEXPRESS;Initial Catalog=test3;User ID=sa;Password=yingjh");
cnn1.Open();
//表
SqlCommand cmd1 = new SqlCommand();
cmd1.Connection = cnn1;
cmd1.CommandText = "select * from T";
SqlDataReader data1;
data1 = cmd1.ExecuteReader();
GridView1.DataSource = data1;
GridView1.DataBind();
cnn1.Close();
//圖
cnn1.Open();
SqlDataAdapter Da = new SqlDataAdapter();
Da.SelectCommand = new SqlCommand("select 時間,[溫度(℃)] from T", cnn1);
DataSet ds = new DataSet();
Da.Fill(ds);
DataView myView = new DataView(ds.Tables[0]);
Chart1.Series["Series1"].Points.DataBindXY(myView, "時間", myView, "溫度(℃)");
cnn1.Close();
cnn1.Dispose();
//狀態(tài)
SqlConnection cnn2 = new SqlConnection();
cnn2.ConnectionString = @"Data Source=YINGJHSHP541\SQLEXPRESS;Initial Catalog=test3;User ID=sa;Password=yingjh";
cnn2.Open();
SqlCommand cmd2 = new SqlCommand();
cmd2.Connection = cnn2;
cmd2.CommandText = "select * from ST";
SqlDataReader data2;
data2 = cmd2.ExecuteReader();
data2.Read();
string a = data2.GetString(0);
switch (a)
{
case "1":
Label2.Text = "打開";
break;
case "0":
Label2.Text = "預(yù)設(shè)";
break;
case "-1":
Label2.Text = "關(guān)閉";
break;
default:
break;
}
Label4.Text = data2.GetString(1) + "℃";
cnn2.Close();
cnn2.Dispose();
}
protected void Button1_Click(object sender, EventArgs e)
{
SqlConnection cnn = new SqlConnection(@"Data Source=YINGJHSHP541\SQLEXPRESS;Initial Catalog=test3;User ID=sa;Password=yingjh");
SqlCommand cmd = new SqlCommand();
cnn.Open();
cmd.Connection = cnn;
//設(shè)置開關(guān)，flag為開關(guān)控制權(quán)
switch (DropDownList1.Text)
{
case "1":
cmd.CommandText = "update ST set STATE='1'" + ",flag='1'";
break;
case "0":
cmd.CommandText = "update ST set STATE='0'" + ",STEMP='" + TextBox1.Text + "',flag='1'";
break;
case "-1":
cmd.CommandText = "update ST set STATE='-1'" + ",flag='1'";
break;
default:
cmd.CommandText = "update ST set STATE='0'" + ",STEMP='" + TextBox1.Text + "',flag='1'";
break;
}
cmd.ExecuteNonQuery();
cnn.Close();
cnn.Dispose();
//溫度
SqlConnection cnn1 = new SqlConnection(@"Data Source=YINGJHSHP541\SQLEXPRESS;Initial Catalog=test3;User ID=sa;Password=yingjh");
cnn1.Open();
//表
SqlCommand cmd1 = new SqlCommand();
cmd1.Connection = cnn1;
cmd1.CommandText = "select * from T";
SqlDataReader data1;
data1 = cmd1.ExecuteReader();
GridView1.DataSource = data1;
GridView1.DataBind();
cnn1.Close();
//圖
cnn1.Open();
SqlDataAdapter Da = new SqlDataAdapter();
Da.SelectCommand = new SqlCommand("select 時間,[溫度(℃)] from T", cnn1);
DataSet ds = new DataSet();
Da.Fill(ds);
DataView myView = new DataView(ds.Tables[0]);
Chart1.Series["Series1"].Points.DataBindXY(myView, "時間", myView, "溫度(℃)");
cnn1.Close();
cnn1.Dispose();
//狀態(tài)
SqlConnection cnn2 = new SqlConnection();
cnn2.ConnectionString = @"Data Source=YINGJHSHP541\SQLEXPRESS;Initial Catalog=test3;User ID=sa;Password=yingjh";
cnn2.Open();
SqlCommand cmd2 = new SqlCommand();
cmd2.Connection = cnn2;
cmd2.CommandText = "select * from ST";
SqlDataReader data2;
data2 = cmd2.ExecuteReader();
data2.Read();
string a = data2.GetString(0);
switch (a)
{
case "1":
Label2.Text = "打開";
break;
case "0":
Label2.Text = "預(yù)設(shè)";
break;
case "-1":
Label2.Text = "關(guān)閉";
break;
default:
break;
}
Label4.Text = data2.GetString(1) + "℃";
cnn2.Close();
cnn2.Dispose();
}
protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
}
protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
{
}
}
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