Create a LiNQ In Every Day

ToLowerInvariant : 返回字符转换为小写的结果，使用固定区域性的大小写规则。

也就是说这个转换与Visual Studio 的设置字体风格一致。

ToLower : 返回字符转换为小写的结果，使用当前区域性的大小写规则。

这个转换与程序代码(上下文)的设置字体风格一致。

static void Main()
{
string text = @"Historically, the world of data and the world of objects" +
@" have not been well integrated. Programmers work in C# or Visual Basic" +
@" and also in SQL or XQuery. On the one side are concepts such as classes," +
@" objects, fields, inheritance, and .NET Framework APIs. On the other side" +
@" are tables, columns, rows, nodes, and separate languages for dealing with" +
@" them. Data types often require translation between the two worlds; there are" +
@" different standard functions. Because the object world has no notion of query, a" +
@" query can only be represented as a string without compile-time type checking or" +
@" IntelliSense support in the IDE. Transferring data from SQL tables or XML trees to" +
@" objects in memory is often tedious and error-prone.";

string searchTerm = "data";

//Convert the string into an array of words
string[] source = text.Split(new char[] { '.', '?', '!', ' ', ';', ':', ',' }, StringSplitOptions.RemoveEmptyEntries);

// Create and execute the query. It executes immediately
// because a singleton value is produced.
// Use ToLowerInvariant to match "data" and "Data"
var matchQuery = from word in source
where word.ToLowerInvariant() == searchTerm.ToLowerInvariant()
select word;

// Count the matches.
int wordCount = matchQuery.Count();
Console.WriteLine("{0} occurrences(s) of the search term /"{1}/" were found.", wordCount, searchTerm);

// Keep console window open in debug mode
Console.WriteLine("Press any key to exit");
Console.ReadKey();
}