C# Academy · Lesson

Ranges with Arrays and Strings

Slice arrays, spans, and substrings.

Lesson 3 of 413 steps

Ranges with Arrays and Strings is a free C# Academy lesson on CoddyKit. This is lesson 3 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.

Slicing Arrays

The most common use of ranges is slicing arrays. array[1..3] returns a new array containing the selected elements.

using System;

int[] data = { 10, 20, 30, 40, 50 };
int[] middle = data[1..3];
Console.WriteLine(string.Join(",", middle)); // 20,30

Array Slices Are Copies

For arrays, a range slice allocates a new array and copies the elements. Mutating the slice does not affect the original.

using System;

int[] original = { 1, 2, 3, 4 };
int[] slice = original[0..2];
slice[0] = 99;
Console.WriteLine(original[0]); // 1 (unchanged)
Console.WriteLine(slice[0]);    // 99

Substrings via Range

The string indexer supports Range, giving you substrings without calling Substring with offsets and lengths.

using System;

string text = "Hello, World";
string hello = text[0..5];
Console.WriteLine(hello); // Hello

From-End String Slices

Combine ranges with ^ to grab the tail of a string, such as a file extension.

using System;

string file = "report.csv";
string ext = file[^3..];
Console.WriteLine(ext); // csv

Single Character with Index

Indexing a string with a single Index returns one char. Use ^1 for the final character.

using System;

string s = "Coddy";
char last = s[^1];
Console.WriteLine(last); // y

Dropping the First or Last

Open-ended ranges make trimming one element trivial: ..^1 drops the last, 1.. drops the first.

using System;

string quoted = "[value]";
string inner = quoted[1..^1];
Console.WriteLine(inner); // value

Splitting a String into Parts

You can split text by a known position using two range slices.

using System;

string code = "2026-05-30";
string year = code[..4];
string month = code[5..7];
string day = code[8..];
Console.WriteLine(year + " / " + month + " / " + day); // 2026 / 05 / 30

Spans for Zero-Copy Slicing

If you want a slice without allocating, use AsSpan(). A span slice is a window over the original memory, not a copy.

using System;

ReadOnlySpan<char> span = "Hello, World".AsSpan();
ReadOnlySpan<char> word = span[7..];
Console.WriteLine(word.ToString()); // World

Ranges in Loops

You can iterate over a sliced array directly with foreach.

using System;

int[] data = { 2, 4, 6, 8, 10 };
foreach (int n in data[1..4])
    Console.Write(n + " "); // 4 6 8
Console.WriteLine();

Bounds Are Checked

Out-of-range slices throw ArgumentOutOfRangeException, so accidental over-reads fail fast instead of corrupting data.

using System;

int[] d = { 1, 2, 3 };
try { var _ = d[1..10]; }
catch (ArgumentOutOfRangeException) { Console.WriteLine("slice out of bounds"); }

A Practical Parser

Here is a tiny parser that extracts a name and domain from an email using ranges and IndexOf.

using System;

string email = "ada@coddy.dev";
int at = email.IndexOf('@');
string user = email[..at];
string domain = email[(at + 1)..];
Console.WriteLine(user + " | " + domain); // ada | coddy.dev

Quick Check

Check your grasp of range slicing on arrays and strings.

Answer it in the interactive lesson

Recap

You learned how ranges apply to arrays and strings.

array[1..3] returns a new copied array.
string[a..b] returns a substring; a single Index returns a char.
..^1 and 1.. trim one element.
AsSpan() slices without allocating.

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Frequently Asked Questions

Is the “Ranges with Arrays and Strings” lesson free?

Yes — the full text of “Ranges with Arrays and Strings” 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 “Ranges with Arrays and Strings”?

Slice arrays, spans, and substrings. 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, so you can start here or from the beginning and move at your own pace. This is lesson 3 of 4.

How long does the “Ranges with Arrays and Strings” 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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