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How do you create and work with a multidimensional (rectangular) array versus a jagged array? What is Span<T> and what core performance problem does it solve? How does Memory<T> differ from Span<T>, and when would you use Memory<T> instead? How do you slice an array or string efficiently without allocating a new array/string, using Span<T> or ReadOnlySpan<T>? What restrictions does the C# compiler enforce on Span<T> because it's a 'ref struct'? How does 'stackalloc' work together with Span<T> to allocate memory on the stack instead of the heap? How would you write a high-performance CSV field parser using ReadOnlySpan<char> that avoids all intermediate string allocations? How does the modern .NET Span-based string.Split (via MemoryExtensions) or manual span-splitting reduce garbage collection pressure compared to string.Split()? How would you use Span<T> to implement an in-place array reversal or sorting algorithm without allocating a temporary array? What is the role of Span<T> and Memory<T> in .NET, and why can't Span<T> be used inside an async method?
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C# › Arrays, Span<T> & Memory<T>

How do you declare and initialize a fixed-size array in C#?

Beginner

Answer

Arrays in C# have a fixed size set at creation time, declared with square brackets after the element type, and can be initialized with a collection expression or explicit 'new' syntax.
int[] numbers = new int[5];
int[] scores = { 90, 85, 78 };
string[] names = new string[] { "Sam", "Alex" };
Real-world example Storing a fixed set of monthly sales figures where the count (12 months) never changes.

Common follow-ups: What's the default value of each element in a newly created int[] array?

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