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📓 Strings, String Concatenation and Interpolation, and Chars

Most of the information we worked with in Introduction to Programming, such as strings, integers, variables, methods, and objects function similarly in C#. There are a few differences but you'll catch on quickly!

In this lesson we'll learn about one of the most common data types, the string. We'll then learn about string concatenation and interpolation. We'll wrap up by learning about the char data type.


C# strings are very similar to JavaScript strings. They're simply a sequence of characters between two quotation marks. Note that strings require quotation marks " specifically — apostrophes (') are used to define a single character for a data type called "char". We'll learn about chars later in this lesson.

We can open our REPL with the $ dotnet-script command in the Terminal (for Mac) or GitBash (for Windows) to try them out.

Once in the REPL we'll type a basic string and hit Enter:

> "Hello World"

Here is the output:

"Hello World"

Now let's try it with a semicolon.

> "Hello World";

Adding a semicolon produces an error:

(1,1): error CS0201: Only assignment, call, increment, decrement, await, and new object expressions can be used as a statement

Remember that C# is a strongly typed language. According to this error, we've already broken one of C#'s strict rules about typing. In this case, the semicolon indicates that C# is expecting a command. In other words, you need to do something with this string. Let's take the error's advice and make an assignment, which means we'll assign our string to a variable:

> string greeting = "Hello";

We're no longer using JavaScript's let or const. Instead, we're being more specific and declaring that greeting is a string. We'll need to do this for all variables that we create — that is, declare its specific data type.

Next, let's call the variable in the REPL:

> greeting

Without the semicolon, our REPL can still return the value of the variable. A quick word of warning: don't get used to solving problems in C# by dropping semicolons. This convention helps us evaluate code in the REPL, nothing more.

String Concatenation

We can also concatenate strings together with the + operator. As you'll recall, concatenation is the act of making a new string out of multiple smaller strings:

> "Hello" + " " + "World"
"Hello World"

Notice the return value is different from what we originally typed. This is the evaluation part of the REPL (Read, Evaluate, Print, Loop) acronym; C# has evaluated the code and returned a result.

Here's another example:

> "Programming" + " " + "is" + " " "awesome!"

(1,34): error CS1002: ; expected

Oops, we got an error this time! The error says a semicolon was expected. Something is wrong with our syntax and the REPL doesn't understand the command.

The issue isn't a missing semicolon, however! This error points us to a missing + between the space after "is" and the string "awesome". Let's fix this:

> "Programming" + " " + "is" + " " + "awesome!"
"Programming is awesome!"

String Interpolation

String interpolation in C# is the same as template literals in JavaScript, where we can include a variable within a string that we create. Here's an example of what this looks like:

> string greeting1 = "Hello";
> $"{greeting1} World!"
"Hello World!"

Here's a few rules for using string interpolation:

  • We indicate that we are going to use string interpolation by include the $ sign before the opening quotes of the string, with no space in between.
  • We surround the variable we want evaluated and added to our string in curly brackets: { }.

For contrast, here's this same code in JavaScript using a template literal:

> const greeting1 = "Hello";
> `${greeting1} World!`;
"Hello World!"


A char is the C# data type that represents a single symbol or alphanumeric character, in upper or lower case. Here's how we can create chars in the REPL:

> 'H'
> '9'
> '/'

Notice that we declare a char with apostrophes and not quotation marks — quotation marks " " are reserved for creating strings, while apostrophes ' ' are reserved for creating chars.

And here's how we can store a char in a variable by declaring it of the type char; this is also called assignment:

> char myGrade = 'B';
> myGrade

Note that we cannot perform concatenation or interpolation with chars!

There we go! Play around with strings and chars a bit more in the REPL before advancing to the next lesson.