2.5. Strings

A string in C# is a collection of literal characters used to store text. In C# string must be enclosed in double quotes to delimit the string.

Since a string is a series of characters (of the char type), we can refer to the individual characters by using index numbers, which can be useful when we need to manipulate strings and character level. In the example below, the character f has an index number of 0.

Index	0	1	2	3	4	5	6
Character	f	o	r	m	o	s	a

When represented in code, indexing works like below:

> string txt = "ilha formosa";
> txt[3]
'a'
>

Note that, in the example above, the output is a character since strings consist of characters and the char type are created by delimiting the characters by single quotation marks.

2.5.1. Creating a String

To create a variable of type string and assign it with a value:

> string dayOfWeek = "Monday";

> dayOfWeek      // the REPL shell prints the variable value
"Monday"
>

In an editor such as VS Code, this would look like the following, where Console.WriteLine prints out the string rather than REPL.

string dayOfWeek = "Monday";

Console.WriteLine(dayOfWeek);   // Console.WriteLine for output

Since this is a console app, we use the TERMINAL in VS Code to do dotnet run to see the project outcome. Make sure you are in the right project directory, though.

2.5.2. String Concatenation

String concatenation is to join stings together. In C#, the + operator is used to perform concatenation. Note C# uses the + operator for both arithmetic addition and concatenation. To concatenate two strings together:

> string firstName = "Tsangyao";    // assign value to variable
> string lastName = " Chen";

> firstName + lastName              // concatenation
"Tsangyao Chen"
>

C# can also concatenate values of different data types. The example below shows you how to concatenate data of string type and int type:

> int aLargeAmountOf = 400;

> "I spent " + aLargeAmountOf + " dollars on coffee this week."
"I spent 400 dollars on coffee this week."
>

2.5.3. Escape Special Characters

Since C# requires double quotation marks as delimiters for creating strings, when we need to show quotation marks as part of a string, the situation becomes tricky. Consider the following string toBe1. We see that there is a syntax error at (1,18) (line# 1, character# 18) when trying to put a quotation inside the string:

> string toBe1 = ""To be, or not to be" is a speech given by Prince Hamlet.";
┌────CompilationErrorException─────┐
│ (1,18): error CS1002: ; expected │
└──────────────────────────────────┘

To make the quotation work, we need to use the special character backslash \ as escape character, meaning that the character following it should be treated specially: They turns special characters into string characters.

> string toBe2 = “"To be, or not to be" is a speech given by Prince Hamlet.”;

> Console.WriteLine(toBe2); “To be, or not to be” is a speech given by Prince Hamlet.

In our example above, the " in \"To be and to be\" are escaped and therefore special character " can be treated as string and shown as intended.

Another example would look like the following.

> Console.WriteLine("Goog morning!");
Goog morning!
> Console.WriteLine("He said, \"Goog morning!\".");
He said, "Goog morning!".

Common special cases to be escaped include:

Escape character	Result
`\"`	`"` (quote)
`\'`	`'` ( single quote in char literal)
`\\`	`\` (backslash)
`\n`	new line
`\t`	new tab

The newline character (\n) inserts a new line and move the cursor to the beginning of the new line. This is useful because C# string literals are characters delimited by double quotation marks " in one line. [1] To print to multiple lines, we use \n like:

> Console.WriteLine("Good morning. Good afternoon. Good evening.");
Good morning. Good afternoon. Good evening.

> Console.WriteLine("Good morning. \nGood afternoon. \nGood evening.");
Good morning.
Good afternoon.
Good evening.

>

2.5.4. String Properties and Methods

Although we use string literals, strings are objects. In object-oriented-programming, objects have instance properties and instance methods. Some examples of C# string properties and methods are:

The length of a string can be found using the Length property:

string txt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
Console.WriteLine("The length of the txt string is: " + txt.Length);

There are many string methods available [2]. As examples, ToUpper() and ToLower() return a copy of the string converted to uppercase or lowercase:

string txt = "Hello World";
Console.WriteLine(txt.ToUpper());   // Outputs "HELLO WORLD"
Console.WriteLine(txt.ToLower());   // Outputs "hello world"

Footnotes