Strings and immutability C# with Example

Immutable types are types that when changed create a new version of the object in memory, rather than changing 
the existing object in memory. The simplest example of this is the built-in string type. 
Taking the following code, that appends " world" onto the word "Hello" 
string myString = "hello"; 
myString += " world"; 
What is happening in memory in this case is that a new object is created when you append to the string in the 
second line. If you do this as part of a large loop, there is the potential for this to cause performance issues in your 
application. 
The mutable equivalent for a string is a StringBuilder 
Taking the following code 
StringBuilder myStringBuilder = new StringBuilder("hello"); 
myStringBuilder.append(" world"); 
When you run this, you are modifying the StringBuilder object itself in memory.