C# Academy · Lesson

Composite Formatting with string.Format

Use indexed placeholders and alignment.

Composite Formatting with string.Format is a free C# Academy lesson on CoddyKit — lesson 2 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.

Composite Formatting

string.Format uses numbered placeholders like {0} and {1} that map to the arguments that follow.

using System;

class Program {
    static void Main() {
        string msg = string.Format("Hello, {0}!", "Ada");
        Console.WriteLine(msg);
    }
}

Multiple Arguments

Each index refers to an argument by position. {0} is the first, {1} the second, and so on.

using System;

class Program {
    static void Main() {
        Console.WriteLine(string.Format("{0} + {1} = {2}", 2, 3, 5));
    }
}

Reusing an Index

You can use the same index more than once to repeat an argument without passing it twice.

using System;

class Program {
    static void Main() {
        Console.WriteLine(string.Format("{0}{0}{0}", "ab"));
    }
}

Format Specifier After Colon

Add a colon and a specifier to control formatting, such as {0:F2} for two decimals.

using System;

class Program {
    static void Main() {
        Console.WriteLine(string.Format("Pi is {0:F2}", 3.14159));
    }
}

Alignment with Comma

A comma and width set alignment: {0,8} right-aligns in eight characters; a negative width left-aligns.

using System;

class Program {
    static void Main() {
        Console.WriteLine(string.Format("[{0,8}]", "hi"));
        Console.WriteLine(string.Format("[{0,-8}]", "hi"));
    }
}

Alignment and Format Together

You can combine both: {0,10:F2} formats to two decimals and right-aligns in ten characters.

using System;

class Program {
    static void Main() {
        Console.WriteLine(string.Format("[{0,10:F2}]", 3.5));
    }
}

Console.WriteLine Formatting

Console.WriteLine accepts the same composite format string and arguments directly.

using System;

class Program {
    static void Main() {
        Console.WriteLine("{0} scored {1} points", "Sam", 42);
    }
}

Building a Table

Alignment makes simple aligned tables easy in console output.

using System;

class Program {
    static void Main() {
        Console.WriteLine(string.Format("{0,-10}{1,5}", "Apples", 3));
        Console.WriteLine(string.Format("{0,-10}{1,5}", "Pears", 12));
    }
}

Interpolation Compiles to This

Behind the scenes, interpolated strings often compile to composite formatting. They are two faces of the same feature.

using System;

class Program {
    static void Main() {
        int n = 5;
        Console.WriteLine(string.Format("n = {0}", n));
        Console.WriteLine($"n = {n}");
    }
}

Escaping Braces

As with interpolation, double a brace to print it literally in a composite format string.

using System;

class Program {
    static void Main() {
        Console.WriteLine(string.Format("{{0}} shows literally, {0} shows value", 7));
    }
}

When to Choose Format

Composite formatting is handy when the template is stored separately, such as in resource files for localization.

using System;

class Program {
    static void Main() {
        string template = "Welcome, {0}";
        Console.WriteLine(string.Format(template, "Lee"));
    }
}

Quick Check

Test your knowledge of composite formatting.

Recap

string.Format uses indexed placeholders ({0}, {1}) mapped to arguments by position, which can be reused. A colon adds format specifiers and a comma sets alignment width.

It powers Console.WriteLine formatting and underlies interpolation, and it is ideal when templates live in separate resources.

Frequently asked questions

Is the “Composite Formatting with string.Format” lesson free?

Yes — the full text of “Composite Formatting with string.Format” 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 “Composite Formatting with string.Format”?

Use indexed placeholders and alignment. 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 2 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Composite Formatting with string.Format” 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.

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