C# String Type

In this chapter you will learn:

1. What is the String type
2. How to create string literal
3. How to compare to string values
4. Escape Sequences
5. Verbatim string literals
6. String concatenation
7. Null and empty strings
8. Accessing characters within a string

Description

C#'s string type represents an immutable sequence of Unicode characters.

Aliasing the System.String type.

string literal

A string literal is specified inside double quotes:

Equality

string is a reference type, rather than a value type. Its equality operators, however, follow value-type semantics:

string a = "test"; 
string b = "test"; 
Console.Write (a == b);  // True 

Escape Sequences

The escape sequences that are valid for char literals also work inside strings:

     string a = "Here's a tab:\t";
     

Verbatim string literals

C# allows verbatim string literals.

A verbatim string literal is prefixed with @ and does not support escape sequences.

The following example shows how to create verbatim string:

 
string a2 = @ "\\server\fileshare\helloworld.cs";

A verbatim string literal can also span multiple lines:

string escaped  = "First Line\r\nSecond Line"; 
string verbatim = @"First Line 
Second Line"; 

You can include the double-quote character in a verbatim literal by writing it twice:

string xml = @"<customer id=""123""></customer>"; 

String concatenation

The + operator concatenates two strings:

string s = "a" + "b"; 

The right hand operand may be a nonstring value, in which case ToString is called on that value. For example:

string s = "a" + 5;  // a5 

Null and empty strings

An empty string has a length of zero.

To create an empty string, you can use either a literal or the static string.Empty field; to test for an empty string, you can either perform an equality comparison or test its Length property:

string empty = "";
Console.WriteLine (empty == "");              // True
Console.WriteLine (empty == string.Empty);    // True
Console.WriteLine (empty.Length == 0);        // True
//from   ww  w.j  a  va 2s. c  om

Because strings are reference types, they can also be null:

string nullString = null;//from w  w  w .j a  va  2  s. com
Console.WriteLine (nullString == null);        // True
Console.WriteLine (nullString == "");          // False
Console.WriteLine (nullString.Length == 0);    // NullReferenceException

The static string.IsNullOrEmpty method is a useful shortcut for testing whether a given string is either null or empty.

String indexer

A string's indexer returns a single character at the given index. As with all functions that operate on strings, this is zero-indexed:

string str  = "abcde";
char letter = str[1];        // letter == 'b'

string also implements IEnumerable<char>, so you can foreach over its characters:

foreach (char c in "123") 
   Console.Write (c + ",");    // 1,2,3,

Next chapter...

What you will learn in the next chapter:

1. How to use Arithmetic Operators
2. Example for C# Arithmetic Operators
3. How to handle Divide by zero exception

C# String Type