String interpolation

C# course · Beginner · Lesson 31/116

Learn to embed variables in text with $"...".

String interpolation

The modern way to embed variables into text is string interpolation. You start the string with a $ prefix and put the variable inside curly braces { }: $"Hello, {name}!".

Without the $ sign, the curly braces are ordinary characters and you would see the variable name, not its value. $"Price: {price} USD" becomes Price: 25 USD. No need for the + operator in between.

Expressions and formatting

Inside the curly braces you can write expressions, not only variables: $"Total: {price * quantity} USD". You can also add a colon for formatting: $"Year: {now:yyyy}" prints just the year.

Formatting controls how numbers and dates look. For example, {price:F2} shows the price with two decimal places. Interpolation thus gives you both value and presentation in one spot.

Exercise Write a greeting message

Declare a name variable with the value "Alex". Then use interpolation to produce "Hello, Alex!" with Console.WriteLine. You must use the $ prefix and {name}.

Show example solution

Write string name = "Alex";, then Console.WriteLine($"Hello, {name}!");
Example solution:
using System;

class Program
{
    static void Main()
    {
        string name = "Alex";
        Console.WriteLine($"Hello, {name}!");
    }
}

Test yourself

Write the interpolation prefix

string name = "Alex";
string greeting = ____ "Hello, {name}!";

Show answer

string name = "Alex";
string greeting = $ "Hello, {name}!";

With string name = "Sam"; what does $"Hello, {name}!" print?
```
string name = "Sam";
Console.WriteLine($"Hello, {name}!");
```
- Hello, {name}!
- Hello, Sam
- Hello, name!
- Hello, Sam!
Show answer

Hello, Sam! — Correct. {name} is replaced by the value and the exclamation stays.
Match each expression to its output

$"{5+3}"

8
$"{5*3}"

15
$"{5-3}"

2
$"{10/2}"

5

String interpolation