Array helper methods

Sorting in place

int[] nums = { 5, 3, 9, 1 };
Array.Sort(nums);            // nums is now { 1, 3, 5, 9 }
Array.Reverse(nums);         // { 9, 5, 3, 1 }

Array.Sort mutates the array — in place — using an introsort; average O(n log n). There's no "sorted copy" overload; if you must keep the original, copy first ((int[])nums.Clone()). Strings sort with culture-aware comparison by default — for code-like ordering say Array.Sort(names, StringComparer.Ordinal).

Searching

int at = Array.IndexOf(nums, 5);      // index or -1 when absent
bool has = Array.Exists(nums, n => n > 8);   // predicate search
int first = Array.Find(nums, n => n > 8);    // element or 0/""/null default

IndexOf returns -1 when absent — a sentinel you must check before indexing with it. The predicate family (Exists/Find/FindAll) takes a lambda; you met lambdas briefly, they get a full module later.

Copying without aliasing

int[] src = { 1, 2, 3, 4 };
int[] dst = new int[src.Length];
src.CopyTo(dst, 0);          // dst is independent
int[] head = new int[2];
src.CopyTo(head, 0);         // first two elements only

CopyTo(target, startInTarget) writes elements into an existing array (which must be long enough). Now aliasing and copying are two visible paths: b = a shares, CopyTo/Clone duplicates. Every time you hand an array to a method or store it in a field, ask: do I want the alias or a copy?