Dictionary key-value collection in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Dictionary in C#?

A Dictionary in C# is a collection that stores data as key-value pairs, where each key is unique and is used to access its corresponding value quickly.

beginner

How do you add an item to a Dictionary in C#?

Use the Add(key, value) method or the indexer syntax dictionary[key] = value; to add a new key-value pair.

intermediate

What happens if you try to add a duplicate key to a Dictionary?

Adding a duplicate key causes an exception because keys must be unique in a Dictionary.

beginner

How can you check if a key exists in a Dictionary?

Use the ContainsKey(key) method which returns true if the key exists, otherwise false.

intermediate

How do you retrieve a value safely from a Dictionary without risking an exception?

Use TryGetValue(key, out value) which returns true if the key exists and outputs the value; otherwise, it returns false.

What type of data structure is a Dictionary in C#?

A Key-value collection

B List of values

C Array of keys

D Stack

A Dictionary stores data as key-value pairs, making it a key-value collection.

Which method checks if a key exists in a Dictionary?

A ContainsKey()

B Exists()

C ContainsValue()

D FindKey()

ContainsKey() checks if a specific key exists in the Dictionary.

What happens if you add a key that already exists in a Dictionary using Add()?

A The Dictionary clears all items

B The value is updated

C The key is ignored

D An exception is thrown

Adding a duplicate key with Add() throws an exception because keys must be unique.

Which method safely retrieves a value from a Dictionary?

A FetchValue()

B GetValue()

C TryGetValue()

D Retrieve()

TryGetValue() safely retrieves a value and avoids exceptions if the key is missing.

How do you add a key-value pair to a Dictionary using indexer syntax?

A dictionary.Add(key, value);

B dictionary[key] = value;

C dictionary.Insert(key, value);

D dictionary.Set(key, value);

Using dictionary[key] = value; adds or updates the key-value pair.

Explain what a Dictionary key-value collection is and how it works in C#.

Think about how you use a real dictionary to find a word's meaning.

Describe how to safely retrieve a value from a Dictionary without causing an error if the key does not exist.

It's like checking if a word exists before reading its meaning.