C# Academy · Lesson

String Interpolation Basics

Embed expressions directly inside strings.

Lesson 1 of 413 steps

String Interpolation Basics is a free C# Academy lesson on CoddyKit. This is lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the C# Academy learning path, and your progress syncs across the web and the CoddyKit app. The C# Academy course includes 4 lessons in total.

Interpolated Strings

An interpolated string starts with a dollar sign before the opening quote. Inside, you place expressions in curly braces, and C# inserts their values.

using System;

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

Embedding Expressions

The braces can hold any expression, not just a variable. C# evaluates it and converts the result to text.

using System;

class Program {
    static void Main() {
        int a = 3, b = 4;
        Console.WriteLine($"Sum is {a + b}");
    }
}

Calling Methods Inside

You can call methods or properties inside the braces, keeping output code compact and readable.

using System;

class Program {
    static void Main() {
        string word = "hello";
        Console.WriteLine($"Upper: {word.ToUpper()}");
    }
}

Interpolation vs Concatenation

Interpolation is usually clearer than chaining many plus signs, especially with several variables.

using System;

class Program {
    static void Main() {
        string first = "Grace", last = "Hopper";
        Console.WriteLine($"{first} {last}");
    }
}

Multiple Placeholders

You can include as many braces as you need in one string.

using System;

class Program {
    static void Main() {
        int day = 5, month = 11, year = 2026;
        Console.WriteLine($"{day}/{month}/{year}");
    }
}

Escaping Braces

To print a literal curly brace, double it. Two opening braces produce one in the output.

using System;

class Program {
    static void Main() {
        int x = 5;
        Console.WriteLine($"Value in braces: {{{x}}}");
    }
}

Format Specifiers

Inside the braces you may add a colon and a format specifier, like a number of decimal places.

using System;

class Program {
    static void Main() {
        double price = 3.14159;
        Console.WriteLine($"Price: {price:F2}");
    }
}

Alignment in Interpolation

A comma plus a number sets alignment width: positive right-aligns, negative left-aligns within that width.

using System;

class Program {
    static void Main() {
        Console.WriteLine($"[{"hi",10}]");
        Console.WriteLine($"[{"hi",-10}]");
    }
}

Ternary Inside Interpolation

Conditional expressions work inside the braces, though wrapping them in parentheses keeps the parser happy.

using System;

class Program {
    static void Main() {
        int n = 7;
        Console.WriteLine($"{n} is {(n % 2 == 0 ? "even" : "odd")}");
    }
}

Building Messages

Interpolation makes user-facing messages easy to read and maintain.

using System;

class Program {
    static void Main() {
        string user = "Lee";
        int items = 3;
        Console.WriteLine($"{user}, you have {items} new messages.");
    }
}

Interpolation Is Compile-Checked

Unlike runtime templates, an interpolated string is checked at compile time, so missing variables are caught early.

using System;

class Program {
    static void Main() {
        int score = 95;
        string grade = score >= 90 ? "A" : "B";
        Console.WriteLine($"Score {score} earns grade {grade}");
    }
}

Quick Check

Test your understanding of string interpolation.

Answer it in the interactive lesson

Recap

Interpolated strings begin with a dollar sign and embed expressions in curly braces, which C# evaluates and converts to text. They are clearer than concatenation and are compile-time checked.

You can add format specifiers and alignment after a colon and comma, and you escape literal braces by doubling them.

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Frequently Asked Questions

Is the “String Interpolation Basics” lesson free?

Yes — the full text of “String Interpolation Basics” is free to read here on the web. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the C# Academy course, upgrade to CoddyKit PRO. The C# Academy course includes 4 lessons in total.

What will I learn in “String Interpolation Basics”?

Embed expressions directly inside strings. You practise C# Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start C# Academy?

No prior experience is required. C# Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 1 of 4.

How long does the “String Interpolation Basics” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this C# Academy lesson?

Yes. Every C# Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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