C# Academy · Lesson

The Range Type and .. Operator

Take slices with range expressions.

The Range Type and .. Operator 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.

Meet the Range Type

System.Range describes a slice of a sequence using a start and an end Index. It pairs perfectly with the range operator .. to express sub-sequences.

using System;

Range r = 1..3;
Console.WriteLine(r.Start + ".." + r.End); // 1..3

The .. (range) Operator

The range operator a..b builds a Range from index a (inclusive) to index b (exclusive). So 1..3 covers positions 1 and 2.

using System;

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

Start Inclusive, End Exclusive

The exclusive end mirrors how for loops work: the number of elements equals end - start. Range 2..5 yields three elements.

using System;

int[] data = { 0, 1, 2, 3, 4, 5, 6 };
int[] slice = data[2..5];
Console.WriteLine(slice.Length);          // 3
Console.WriteLine(string.Join(",", slice)); // 2,3,4

Open-Ended Ranges

You may omit either bound. ..3 means "from the start up to 3", and 2.. means "from 2 to the end". .. alone copies the whole sequence.

using System;

int[] d = { 10, 20, 30, 40, 50 };
Console.WriteLine(string.Join(",", d[..3])); // 10,20,30
Console.WriteLine(string.Join(",", d[2..])); // 30,40,50
Console.WriteLine(string.Join(",", d[..]));  // 10,20,30,40,50

Ranges with From-End Indices

Combine .. with ^ to slice relative to the end. ^2.. means "the last two elements".

using System;

int[] d = { 1, 2, 3, 4, 5 };
Console.WriteLine(string.Join(",", d[^2..]));  // 4,5
Console.WriteLine(string.Join(",", d[..^1]));  // 1,2,3,4 (drop last)

Range as a Stored Value

A Range is a value you can name and reuse across different collections of the same length convention.

using System;

Range middle = 1..^1; // drop first and last
int[] a = { 0, 1, 2, 3, 4 };
Console.WriteLine(string.Join(",", a[middle])); // 1,2,3

Range.GetOffsetAndLength

To resolve a range against a concrete length, call GetOffsetAndLength(length). It returns the start offset and the slice length, handling from-end indices for you.

using System;

Range r = ^3..^1;
var (offset, length) = r.GetOffsetAndLength(5);
Console.WriteLine(offset + " " + length); // 2 2

Range.All

The static Range.All is the same as .. and selects the entire sequence. It is handy when passing ranges as arguments.

using System;

Range whole = Range.All;
int[] d = { 9, 8, 7 };
Console.WriteLine(string.Join(",", d[whole])); // 9,8,7

Constructing Range Explicitly

Besides the operator, you can call the constructor or factory methods Range.StartAt and Range.EndAt for clarity.

using System;

Range a = new Range(1, 3);
Range b = Range.StartAt(2);
Range c = Range.EndAt(2);
Console.WriteLine(a + " | " + b + " | " + c);

Empty and Invalid Ranges

A range where start equals end produces an empty slice. A range whose start is past its end (after resolving) throws at slice time.

using System;

int[] d = { 1, 2, 3, 4 };
Console.WriteLine(d[2..2].Length); // 0 (empty)
try { var _ = d[3..1]; }
catch (ArgumentOutOfRangeException) { Console.WriteLine("invalid range"); }

Putting It Together

Ranges make text and array processing concise. Here we grab a window in the middle of an array without any index arithmetic.

using System;

int[] readings = { 5, 7, 9, 11, 13, 15 };
int[] window = readings[1..^1];
Console.WriteLine(string.Join(",", window)); // 7,9,11,13

Quick Check

Make sure you understand the range operator semantics.

Recap

You learned that System.Range describes a slice with the .. operator.

Start is inclusive, end is exclusive: count = end - start.
Bounds are optional: ..3, 2.., ...
.. combines with ^ for from-end slicing.
GetOffsetAndLength(length) resolves a range to concrete numbers.

Frequently asked questions

Is the “The Range Type and .. Operator” lesson free?

Yes — the full text of “The Range Type and .. Operator” 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 “The Range Type and .. Operator”?

Take slices with range expressions. 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 “The Range Type and .. Operator” 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.

Can I write and run code in this C# Academy lesson?

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