C# Academy · Lesson

String Interpolation Basics

Embed expressions directly inside strings.

String Interpolation Basics is a free C# Academy lesson on CoddyKit — 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, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

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.

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.

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, and the C# Academy course includes 4 lessons in total. 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.

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; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.

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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