C# Academy · Lesson

Composite Formatting with string.Format

Use indexed placeholders and alignment.

Lesson 2 of 413 steps

Composite Formatting with string.Format is a free C# Academy lesson on CoddyKit. This is 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, and your progress syncs across the web and the CoddyKit app. The C# Academy course includes 4 lessons in total.

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.

Answer it in the interactive lesson

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.

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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. 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 “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.

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