List generic collection in C Sharp (C#) - Step-by-Step Execution

Concept Flow - List generic collection

Create List<T> instance

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Add elements to List

↓

Access elements by index

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Modify elements

↓

Remove elements

↓

Iterate over List

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Use List methods (Count, Clear, Contains)

This flow shows how a List<T> is created, elements are added, accessed, modified, removed, and iterated with built-in methods.

Execution Sample

C Sharp (C#)

List<int> numbers = new List<int>();
numbers.Add(10);
numbers.Add(20);
numbers.Add(30);
int first = numbers[0];
numbers[1] = 25;
numbers.Remove(30);

This code creates a list of integers, adds three numbers, accesses the first element, modifies the second, and removes the number 30.

Execution Table

Step	Operation	List Content	Index Access/Modification	Result/Effect
1	Create empty List<int>	[]	-	List initialized with 0 elements
2	Add 10	[10]	-	10 added at index 0
3	Add 20	[10, 20]	-	20 added at index 1
4	Add 30	[10, 20, 30]	-	30 added at index 2
5	Access first element	[10, 20, 30]	numbers[0]	Returns 10
6	Modify second element	[10, 25, 30]	numbers[1] = 25	20 changed to 25
7	Remove element 30	[10, 25]	-	30 removed from list

💡 All operations complete; list now contains [10, 25]

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	After Step 7
numbers	[]	[10]	[10, 20]	[10, 20, 30]	[10, 20, 30]	[10, 25, 30]	[10, 25]
first	undefined	undefined	undefined	undefined	10	10	10

Key Moments - 3 Insights

Why does numbers[1] = 25 change the list element instead of adding a new one?

Because accessing by index with assignment replaces the existing element at that position, it does not add a new element. See step 6 in execution_table where the list changes from [10, 20, 30] to [10, 25, 30].

What happens if we try to access an index that does not exist?

Accessing an index outside the list range causes an error. In the example, we only access numbers[0] which exists. Trying numbers[3] would cause an exception.

How does Remove(30) know which element to remove?

Remove searches the list for the first occurrence of the value 30 and removes it. In step 7, it removes the last element 30, changing the list to [10, 25].

Visual Quiz - 3 Questions

Look at the execution_table at step 5, what value does numbers[0] return?

A 10

B 20

C 25

D 30

💡 Hint

Refer to step 5 in execution_table where numbers[0] is accessed and returns 10.

At which step does the list change from [10, 20, 30] to [10, 25, 30]?

A Step 4

B Step 5

C Step 6

D Step 7

💡 Hint

Check step 6 in execution_table where numbers[1] is modified to 25.

If we add numbers.Add(40) after step 7, what will the list content be?

A [10, 25]

B [10, 25, 40]

C [40, 10, 25]

D [10, 25, 30, 40]

💡 Hint

After step 7, list is [10, 25]. Adding 40 appends it at the end.

Concept Snapshot

List<T> is a resizable array.
Use Add() to append elements.
Access elements by index (zero-based).
Modify elements by assigning to index.
Remove elements by value or index.
Use Count to get number of elements.

Full Transcript

This visual trace shows how a List<int> is created and manipulated step-by-step. We start with an empty list, add three numbers 10, 20, and 30. Then we access the first element which is 10. Next, we modify the second element from 20 to 25. Finally, we remove the element 30. The variable tracker shows how the list content changes after each operation. Key moments clarify common confusions like modifying vs adding elements and how Remove works. The quiz tests understanding of list content at different steps and effects of operations.