Dictionary methods and access patterns in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the ContainsKey method in a C# Dictionary?

The ContainsKey method checks if a specific key exists in the dictionary. It returns true if the key is found, otherwise false.

beginner

How do you safely retrieve a value from a Dictionary without risking an exception if the key is missing?

Use the TryGetValue method. It attempts to get the value for a key and returns true if successful, otherwise false. This avoids exceptions if the key is not present.

beginner

What happens if you try to access a Dictionary value using a key that does not exist with the indexer syntax (e.g., dict[key])?

Accessing a non-existent key with the indexer throws a KeyNotFoundException. To avoid this, use TryGetValue or check with ContainsKey first.

beginner

Which Dictionary method removes a key and its associated value?

The Remove method deletes the key-value pair from the dictionary. It returns true if the key was found and removed, otherwise false.

beginner

How can you iterate over all keys and values in a Dictionary?

Use a foreach loop over the dictionary. Each item is a KeyValuePair<TKey, TValue> where you can access Key and Value properties.

Which method checks if a key exists in a C# Dictionary?

A TryGetValue

B Add

C Remove

D ContainsKey

The ContainsKey method returns true if the key exists in the dictionary.

What does TryGetValue return if the key is not found?

A Throws an exception

B Returns false

C Returns null

D Returns true

TryGetValue returns false if the key is missing, avoiding exceptions.

What exception is thrown when accessing a missing key with dict[key]?

A KeyNotFoundException

B NullReferenceException

C IndexOutOfRangeException

D InvalidOperationException

Accessing a missing key with the indexer throws a KeyNotFoundException.

Which method removes a key-value pair from a Dictionary?

A Add

B Clear

C Remove

D ContainsKey

Remove deletes the key and its value from the dictionary.

How do you access the key and value inside a foreach loop over a Dictionary?

A item.Key and item.Value

B item[0] and item[1]

C item.KeyValue

D item.GetKey() and item.GetValue()

Each item is a KeyValuePair where you use Key and Value properties.

Explain how to safely get a value from a Dictionary when you are not sure if the key exists.

Think about a method that returns true or false and gives you the value if it exists.

Describe how to remove an item from a Dictionary and how to check if the removal was successful.

Focus on the method that deletes a key-value pair and what it returns.