Strings & Characters

Double Quotes

Strings can only use double quotes.
Single quotes can only be used with individual/single characters.

string myString = "All strings must be in double quotes"; 
char myChar = 's';  

System.Char

The System.Char data type is a value data type.
A char represents a single UNICODE character and occuppies two bytes.
The value of a char object is a 16-bit numerical value.
A character literal is specified within single quotes.

System.Char myChar = 'A';  

System.String

The System.String data type is a reference data type.
This is a read-only collections of char objects.
The length property returns the number of char objects that it contains.
A string literal is specified within double quotes

System.String myString = "some text"; 
string myString2 = "some text"; 

Declaring

All Strings should be initialised when they are declared.
If string variables are not initialised they are given the value null by default.

System.String myString1; 
System.String myString1 = null; 
string myString2; 
string myString2 = null; 

Initialising

All strings should be initialised before they are used.
The empty string is an instance of the System.String object that contains zero characters.

System.String myString1 = System.String.Empty; 
string myString2 = string.Empty; 

Empty vs ""

Since .NET 2.0 the following two lines are equivalent.

System.String myString1 = ""; 
System.String myString2 = System.String.Empty; 

Null

You should only assign the keyword null to a string when you want to represent an unassigned object.
The null keyword is the default value when a String variables has not been initialised.
Any attempt to call a method on a null string will generate a NullReferenceException.

Checking for Null

There are a couple of ways you can check for a null value.
System.String myString = null;

if (myString == null) { } 
if (System.String.IsNullOrEmpty(myString)) { }   // added in .NET 3.5 
if (System.String.IsNullOrWhiteSpace(myString)) { }    // added in .NET 4.0 

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