How to Format String in C#: Simple Syntax and Examples

In C#, you can format strings using string interpolation with $"...", the String.Format() method, or composite formatting with placeholders like {0}. These methods let you insert variables and control how values appear inside strings easily.

Syntax

There are three common ways to format strings in C#:

• String Interpolation: Use $"...{variable}..." to embed variables directly.
• String.Format method: Use String.Format("...{0}...", value) with placeholders.
• Composite Formatting: Use placeholders like {index[,alignment][:formatString]} inside strings.

csharp

string name = "Alice";
int age = 30;

// String Interpolation
string s1 = $"Name: {name}, Age: {age}";

// String.Format method
string s2 = String.Format("Name: {0}, Age: {1}", name, age);

// Composite Formatting with alignment and format
string s3 = String.Format("Name: {0,-10} Age: {1:D3}", name, age);

Example

This example shows how to use string interpolation and String.Format to create formatted strings with variables.

csharp

using System;

class Program
{
    static void Main()
    {
        string product = "apple";
        double price = 1.2345;
        int quantity = 5;

        // Using string interpolation
        string message1 = $"You bought {quantity} {product}s for {price:C2} each.";

        // Using String.Format
        string message2 = String.Format("You bought {0} {1}s for {2:C2} each.", quantity, product, price);

        Console.WriteLine(message1);
        Console.WriteLine(message2);
    }
}

Output

You bought 5 apples for $1.23 each.
You bought 5 apples for $1.23 each.

Common Pitfalls

Common mistakes when formatting strings in C# include:

• Forgetting the $ before the string when using interpolation.
• Using incorrect placeholder indexes in String.Format.
• Not matching the number of placeholders with the number of arguments.
• Misusing format specifiers or alignment syntax.

csharp

string name = "Bob";
int score = 95;

// Wrong: missing $ for interpolation
// string wrong1 = "Name: {name}, Score: {score}"; // prints placeholders literally

// Correct:
string right1 = $"Name: {name}, Score: {score}";

// Wrong: placeholder index mismatch
// string wrong2 = String.Format("Name: {0}, Score: {1}", name); // throws error

// Correct:
string right2 = String.Format("Name: {0}, Score: {1}", name, score);

Quick Reference

Method	Syntax	Description
String Interpolation	$"Hello, {name}!"	Embed variables directly inside strings.
String.Format	String.Format("Hello, {0}!", name)	Use placeholders with index numbers.
Composite Formatting	"{0,-10} {1:C2}"	Format alignment and numeric formats.

Key Takeaways

Use string interpolation with $"...{variable}..." for simple and readable formatting.

String.Format allows flexible formatting with numbered placeholders.

Always match placeholders with the correct number of arguments to avoid errors.

Use format specifiers to control number, date, and alignment display.

Remember to prefix strings with $ when using interpolation to embed variables.