Naming rules for Csharp variables
The first character of a variable must be: letter, underscore, Chinese character, or @
The first character can be followed by letters, numbers, underscores, or Chinese characters
Variable name cannot be the same as keyword
Eg: variable names cannot take these keywords such as int, double, if, using, namespace, and so on.
Because these guys already have a special meaning, if you really want to take the keyword as the variable name, you can use @ int, @ double, and so on.
C# variable names are strictly case-sensitive
