Array methods (Sort, Reverse, IndexOf) in C Sharp (C#) - Step-by-Step Execution

Concept Flow - Array methods (Sort, Reverse, IndexOf)

Start with array

↓

Choose method: Sort, Reverse, or IndexOf

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Sort: rearrange elements ascending

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Reverse: flip elements order

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IndexOf: find position of element

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Return result or modify array

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End

Start with an array, pick a method (Sort, Reverse, IndexOf), then either rearrange elements or find an element's position, and finally get the result.

Execution Sample

C Sharp (C#)

int[] numbers = {3, 1, 4, 1, 5};
Array.Sort(numbers);
Array.Reverse(numbers);
int pos = Array.IndexOf(numbers, 1);

Sorts the array ascending, reverses it, then finds the index of the first '1'.

Execution Table

Step	Action	Array State	IndexOf Search Element	IndexOf Result
1	Initial array	[3, 1, 4, 1, 5]	-	-
2	Sort array ascending	[1, 1, 3, 4, 5]	-	-
3	Reverse array	[5, 4, 3, 1, 1]	-	-
4	IndexOf search for 1	[5, 4, 3, 1, 1]	1	3
5	End	[5, 4, 3, 1, 1]	-	-

💡 IndexOf found element '1' at position 3, execution ends.

Variable Tracker

Variable	Start	After Sort	After Reverse	After IndexOf
numbers	[3,1,4,1,5]	[1,1,3,4,5]	[5,4,3,1,1]	[5,4,3,1,1]
pos	undefined	undefined	undefined	3

Key Moments - 3 Insights

Why does IndexOf return 3 instead of 1 when searching for '1'?

Because after sorting and reversing, the first '1' is at index 3 in the modified array (see execution_table step 4).

Does Array.Sort change the original array or create a new one?

Array.Sort changes the original array in place, as shown by the array state changing from step 1 to step 2.

What happens if the element searched by IndexOf is not in the array?

IndexOf returns -1 to indicate the element is not found, but in this example the element '1' is found at index 3.

Visual Quiz - 3 Questions

Look at the execution table, what is the array state after the Reverse method?

A [3, 1, 4, 1, 5]

B [5, 4, 3, 1, 1]

C [1, 1, 3, 4, 5]

D [1, 3, 4, 5, 1]

💡 Hint

Check the 'Array State' column at step 3 in the execution_table.

At which step does the array get sorted in ascending order?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Action' column and array changes between step 1 and 2.

If we searched for '2' using IndexOf instead of '1', what would be the result?

A -1

B 3

C 0

D 4

💡 Hint

Recall that IndexOf returns -1 if the element is not found in the array.

Concept Snapshot

Array methods in C#:
- Array.Sort(array): sorts elements ascending in place.
- Array.Reverse(array): reverses elements order in place.
- Array.IndexOf(array, value): returns first index of value or -1 if not found.
These methods modify the original array except IndexOf which returns a position.

Full Transcript

We start with an array of numbers. First, Array.Sort rearranges the elements in ascending order, changing the array from [3,1,4,1,5] to [1,1,3,4,5]. Next, Array.Reverse flips the array order to [5,4,3,1,1]. Then, Array.IndexOf searches for the first occurrence of '1' in the reversed array and finds it at index 3. The variable 'pos' stores this index. The array methods Sort and Reverse change the original array directly, while IndexOf returns the position of the searched element or -1 if not found.