如何修改和读取app.config文件？网上找的格式和这个都不一样，有劳前辈了！
读取IS_SQLConnString和(Local)
写入连接字符串
请指点！
app.config文件代码如下

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<connectionStrings>
<add name="IS_SQLConnString" connectionString="server=(Local);database=InformationSystem_2012;uid=sa;pwd=qjw159" />
<add name="other" connectionString="其他数据库的连接字符串" />
</connectionStrings>
</configuration>

[解决办法]
ConfigurationManager.ConnectionStrings["IS_SQLConnString"].ConnectionString

需要引入System.Configuration
[解决办法]
用XmlElement element=xmlDoc.SelectSingleNode(@"/configuration/connectionStrings/add[@name='IS_SQLConnString']") as XmlElement;
获取第一个连接字符串的add元素，用element.SetAttribute方法修改其属性的值。
[解决办法]

C# code

        public static void SetValue(string AppKey, string AppValue)        {            XmlDocument xDoc = new XmlDocument();            //加载app.config            xDoc.Load("..\\..\\app.config");            XmlNode xNode = xDoc.SelectSingleNode("//connectionStrings");            XmlElement oldElement = (XmlElement)xNode.SelectSingleNode("//add[@name='" + AppKey + "']");            if (oldElement != null)            {                oldElement.SetAttribute("connectionString", AppValue);            }            else            {                XmlElement newElement = xDoc.CreateElement("add");                newElement.SetAttribute("name", AppKey);                newElement.SetAttribute("connectionString", AppValue);                xNode.AppendChild(newElement);            }            xDoc.Save("..\\..\\app.config");        }