The string data type is used to store string constants. They are delimited by double quotes.
string a = "Hello";
String Concatenation
The concatenation operator
(+) can combine strings together. It also has an accompanying assignment operator (+=), which appends a string to another and creates a new string.
string b = a + " World"; // Hello World
a += " World"; // Hello World
When one of the operands is not of a string type, the concatenation operator will implicitly convert the non-string type into a string, making the following assignment valid.
int i = 1;
string c = i + " is " + 1; // 1 is 1
The string conversion is performed implicitly using the ToString method
. All types in .NET have this method, which provides a string representation of a variable or expression. As seen in the next example, the string conversion can also be made explicitly.
string d = i.ToString() + " is " + 1.ToString(); // 1 is 1
Another way to compile strings is to use string interpolation. This feature was added in C# 6.0 and enables expressions placed inside curly brackets to be evaluated within a string. To perform string interpolation, a dollar sign ($) is placed before the string.
string s1 = "Hello";
string s2 = "World";
string s = $"{s1} {s2}"; // Hello World
Escape Characters
A statement can be broken up across multiple lines, but a string constant must be on a single line. In order to divide it, the string constant has to first be split up using the concatenation operator.
string myString
= "Hello " +
"World";
To add new lines into the string itself, the escape character (
) is used.
string myString = "Hello
World";
This backslash notation is used to write special characters, such as a backslash or double quote. Among the special characters is also a Unicode character notation for writing any character.
Character | Meaning | Character | Meaning |
|---|---|---|---|
| Newline | f | Form feed |
| Horizontal tab | a | Alert sound |
v | Vertical tab | ' | Single quote |
Backspace | " | Double quote | |
| Carriage return | \ | Backslash |
| Null character | uFFFF | Unicode character (four-digit hex number) |
Escape characters can be ignored by adding an @ symbol before the string. This is called a verbatim string
and can be used to make file paths more readable, for example.
string s1 = "c:\Windows\System32\cmd.exe";
string s2 = @"c:WindowsSystem32cmd.exe";
String Compare
The way to compare two strings is simply by using the equal to operator (==). This will not compare the memory addresses, as in some other languages such as Java.
string greeting = "Hi";
bool b = (greeting == "Hi"); // true
String Members
The string type is an alias for the String class. As such, it provides a multitude of methods related to strings, for example, methods like Replace, Insert, and Remove. An important thing to note is that there are no methods for changing a string. Methods that appear to modify a string actually always return a completely new string. This is because the String class is immutable. The content of a string variable cannot be changed unless the whole string is replaced.
string a = "String";
string b = a.Replace("i", "o"); // Strong
b = a.Insert(0, "My "); // My String
b = a.Remove(0, 3); // ing
b = a.Substring(0, 3); // Str
b = a.ToUpper(); // STRING
int i = a.Length; // 6
StringBuilder Class
StringBuilder is a mutable string class. Because of the performance cost associated with replacing a string, the StringBuilder class is a better alternative when a string needs to be modified many times.
System.Text.StringBuilder sb = new
System.Text.StringBuilder("Hello");
The class has several methods that can be used to manipulate the actual content of a string, such as Append, Remove, and Insert.
sb.Append(" World"); // Hello World
sb.Remove(0, 5); // World
sb.Insert(0, "Bye"); // Bye World
To convert a StringBuilder object back into a regular string, you use the ToString method.
string s = sb.ToString(); // Bye World