1. string
Remember that string takes fixing memory until the program ends.
Null and Empty
In C#, a variable's value is null if it is not set, or if it has been explicitly set to null. A null value typically means the value is not known, or has not yet been set, and is frequently a source of errors in programs, because methods cannot be invoked on null instances of types. An empty string is simply a string with a length of zero. It's a valid instance of a string, but one that currently has no characters in it.
It shows how null can cause an exception. String.IsNullOrEmpty(emptyString) can help.
Some API:
Replacing Parts of Strings
The @:
Date and Time：
Refer to：Working with Dates and Times
Convert type：
Logical Expressions:
It is totally same as it is in C++.
