How is a hashtable used in C#?

In C#, a Hashtable is a collection of key/value pairs that is a non-generic collection class. Hashtables use a hash table data structure to store keys and values, allowing for quick access and retrieval of values based on keys.

The usage of Hashtable includes:

1. Add elements: You can add key-value pairs to the Hashtable using the Add() method.
2. Access elements: Values in the Hashtable can be accessed using keys, using either the indexer ([]) or the TryGetValue() method.
3. Remove elements: You can delete elements from Hashtable using the Remove() method based on the key.
4. To check if a key exists: You can use the ContainsKey() method to determine if a Hashtable contains a specified key.
5. Check if a value exists: You can use the ContainsValue() method to determine if a Hashtable contains a specific value.
6. Iterate through elements: You can use a foreach loop to iterate through all elements in the Hashtable.
7. Empty Hashtable: You can use the Clear() method to remove all elements from the Hashtable.
8. You can obtain a collection of keys or a collection of values by using the Keys property to get all the keys in the Hashtable, and the Values property to get all the values in the Hashtable.

It is important to note that Hashtable is a non-generic collection, so it can store keys and values of any type.