Dictionary key-value collection in C Sharp (C#) - Step-by-Step Execution

Concept Flow - Dictionary key-value collection

Create empty Dictionary

↓

Add key-value pairs

↓

Access value by key

↓

Update value by key

↓

Remove key-value pair

↓

Check if key exists

↓

End

This flow shows how a Dictionary is created, used to store key-value pairs, accessed, updated, and managed.

Execution Sample

C Sharp (C#)

var dict = new Dictionary<string, int>();
dict["apple"] = 3;
dict["banana"] = 5;
int count = dict["apple"];
dict["apple"] = 4;
dict.Remove("banana");

This code creates a dictionary, adds two fruits with counts, reads a count, updates a count, and removes a fruit.

Execution Table

Step	Action	Dictionary State	Variable 'count' Value
1	Create empty dictionary	{}	N/A
2	Add key 'apple' with value 3	{"apple":3}	N/A
3	Add key 'banana' with value 5	{"apple":3, "banana":5}	N/A
4	Read value for key 'apple'	{"apple":3, "banana":5}	3
5	Update value for key 'apple' to 4	{"apple":4, "banana":5}	3
6	Remove key 'banana'	{"apple":4}	3

💡 All steps executed; dictionary now has one key 'apple' with value 4.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6
dict	{}	{"apple":3}	{"apple":3, "banana":5}	{"apple":3, "banana":5}	{"apple":4, "banana":5}	{"apple":4}
count	N/A	N/A	N/A	3	3	3

Key Moments - 3 Insights

Why does 'count' keep the old value 3 even after updating 'apple' to 4?

Because 'count' was assigned before the update (Step 4), it holds the old value. The dictionary update (Step 5) does not change 'count' automatically.

What happens if you try to access a key that does not exist?

Accessing a non-existent key throws an exception. You must check if the key exists before accessing it to avoid errors.

Does removing a key affect other keys in the dictionary?

No, removing 'banana' only deletes that key-value pair. Other keys like 'apple' remain unchanged.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'count' after Step 4?

A 3

B 4

C 5

D N/A

💡 Hint

Check the 'Variable 'count' Value' column at Step 4 in the execution table.

At which step is the key 'banana' removed from the dictionary?

A Step 4

B Step 6

C Step 5

D Step 3

💡 Hint

Look at the 'Action' column for the removal operation in the execution table.

If you add a new key 'orange' with value 7 after Step 6, what will the dictionary state be?

A {"apple":4, "banana":5, "orange":7}

B {"banana":5, "orange":7}

C {"apple":4, "orange":7}

D {"orange":7}

💡 Hint

After Step 6, 'banana' is removed, so adding 'orange' adds to existing keys.

Concept Snapshot

Dictionary key-value collection in C#:
- Create with: var dict = new Dictionary<TKey, TValue>();
- Add/update: dict[key] = value;
- Access: value = dict[key];
- Remove: dict.Remove(key);
- Check key: dict.ContainsKey(key);
Keys are unique; values can be updated anytime.

Full Transcript

This visual execution shows how a Dictionary in C# works step-by-step. We start by creating an empty dictionary. Then we add two key-value pairs: 'apple' with 3 and 'banana' with 5. Next, we read the value for 'apple' and store it in a variable 'count'. After that, we update the value for 'apple' to 4. Finally, we remove the key 'banana'. The variable 'count' keeps the old value 3 because it was assigned before the update. Removing 'banana' does not affect 'apple'. This trace helps understand how dictionaries store and manage key-value pairs in C#.