C#连接数据库怎么将App.config连接改为用sqlconnection连接

这是App.config

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
    </startup>
  <connectionStrings>
    <add name="sqlserver" connectionString="Server=127.0.0.1;Initial Catalog=Hotel;User ID=sa;Password=1234" providerName="System.Data.SqlClient" />
  </connectionStrings>
</configuration>

怎么改成下面这种

string connstring = "Server=.; user Id = sa; Pwd = 1234; DataBase = Library";//Data Source =172.20.10.5;Initial Catalog = Library;User ID= sa;Pwd=1234
            SqlConnection conn = new SqlConnection(connstring);
            string sql = String.Format("select count(*) from [Manager] where managerid='{0}' and managerPassword='{1}' and mIdentity='{2}'", username, passworld,midentity );

App.config只是用来存储写好的sql字符串，方便项目所有的连接字符串统一管理，一般这样用
string connstring = ConfigurationManager.ConnectionStrings["sqlserver"].ConnectionString;（取出App.config的connectionStrings里name为sqlserver的ConnectionString字符串）

将app.config中6、7、8行删除
将C#代码中的
string connstring = ConfigurationManager.ConnectionStrings["sqlserver"].ConnectionString;
改为
string connstring = "Server=.; user Id = sa; Pwd = 1234; DataBase = Library";

App.Config是配置文件，将连接字符写在配置文件中便于管理。你可以将连接字符串直接硬编码到你的代码中，也可以通过ConfigurationManager来获取。

string connstring = "Server=127.0.0.1;Initial Catalog=Hotel;User ID=sa;Password=1234";//Data Source =172.20.10.5;Initial Catalog = Library;User ID= sa;Pwd=1234
            SqlConnection conn = new SqlConnection(connstring);
//下面修改你的查询语句
            string sql = String.Format("select count(*) from [Manager] where managerid='{0}' and managerPassword='{1}' and mIdentity='{2}'", username, passworld,midentity );

改成第二种有何作用？

要怎么改。私信

string connstring = System.Configuration.ConfigurationManager.ConnectionStrings["sqlserver"].ConnectionString;

直接在代码里改就行了，把配置文件中的连接参数删除

string connstring = "driver={Sql Server};Server=.;Database=Hotel;UID=sa;PWD=1234";
            SqlConnection conn = new SqlConnection(connstring);
            string sql = String.Format("select count(*) from [Manager] where managerid='{0}' and managerPassword='{1}' and mIdentity='{2}'", username, passworld,midentity );