C# String Operations and Formatting Explained

Strings are one of the most commonly used data types in C#. Whether you’re building user interfaces, logging output, or processing data — you’ll be working with text all the time. Understanding how to manipulate, format, and work with strings is essential for writing clean, efficient C# code.

Here we will cover the most useful string operations, including concatenation, interpolation, formatting, and built-in string methods. You’ll also learn best practices for comparing and handling strings effectively.

If you’re up to scratch on the basics why not move onto my Complete Guide to String Formatting in C#

🧵 What is a String in C#?

A string is a sequence of characters, enclosed in double quotes:

string greeting = "Hello, world!";

Strings in C# are immutable, meaning once created, they can’t be changed — but you can create modified copies using operations.

🔗 String Concatenation

➕ Using + Operator:

string firstName = "Alice";
string lastName = "Smith";
string fullName = firstName + " " + lastName;
Console.WriteLine(fullName); // Alice Smith

💡 Concatenation creates a new string, not a modification of the original.

🧠 String Interpolation (Modern & Clean)

String interpolation is a clearer, preferred way to insert values into strings:

string name = "James";
int score = 95;
Console.WriteLine($"Player {name} scored {score} points.");

Just prefix the string with $ and use {} placeholders.

🧰 Common String Methods

Here are some of the most useful built-in methods:

🔸 Example:

string product = "  Keyboard ";
Console.WriteLine(product.Trim().ToUpper()); // KEYBOARD

🔍 Comparing Strings

C# strings are case-sensitive by default:

string a = "hello";
string b = "Hello";

bool isEqual = a == b; // false

For case-insensitive comparison:

bool match = a.Equals(b, StringComparison.OrdinalIgnoreCase); // true

✅ Use StringComparison.OrdinalIgnoreCase when user input might vary in case.

🔢 String Formatting with string.Format()

A powerful method for templating:

string formatted = string.Format("Hello {0}, your balance is {1:C}", "Alex", 123.45);
// Output: Hello Alex, your balance is £123.45

Use {0}, {1}, etc. as placeholders. You can also format numbers and dates.

📦 Splitting and Joining Strings

🔸 Split:

string csv = "apple,banana,grape";
string[] fruits = csv.Split(',');

foreach (string fruit in fruits)
{
    Console.WriteLine(fruit);
}

🔸 Join:

string[] names = { "Alice", "Bob", "Charlie" };
string result = string.Join(" | ", names);
// Output: Alice | Bob | Charlie

🧠 StringBuilder (Advanced)

When building long or complex strings, use StringBuilder for better performance:

using System.Text;

StringBuilder sb = new StringBuilder();
sb.Append("Hello");
sb.Append(" ");
sb.Append("World!");
Console.WriteLine(sb.ToString());

✅ Ideal for loops or large dynamic strings.

🧪 Practice Exercise

Write a method that:

• Accepts a user’s full name
• Returns it formatted as: LASTNAME, Firstname
• Handles extra spaces and capitalisation

static string FormatName(string fullName)
{
    string trimmed = fullName.Trim();
    string[] parts = trimmed.Split(' ');

    if (parts.Length >= 2)
    {
        string first = char.ToUpper(parts[0][0]) + parts[0].Substring(1).ToLower();
        string last = parts[1].ToUpper();
        return $"{last}, {first}";
    }
    return fullName;
}

📚 Summary

📬 Want help with text manipulation or need a hand preparing for interviews and assessments? Contact us — we’re always happy to help with code questions, project support, or personalised learning plans.