Records

A record is a collection of related data items, each called a field. Unlike an array, a record can store different data types in each field. Records are often used to represent real-world entities such as a student, employee, or book.

Example — a student record

Each field in a record has a name and a data type. Records are the basis for rows in database tables.

Accessing record fields

student.firstName ← "Priya"
OUTPUT student.studentID

Hash Tables

A hash table is a data structure that stores key-value pairs and uses a hash function to compute an index (address) for each key. This allows for very fast data retrieval — ideally O(1) — by calculating where data is stored rather than searching through it.

How a hash function works

1. Take the key (e.g., "Alice" or the number 42)
2. Apply the hash function to produce an integer index
3. Store the value at that index in the array
4. To look up a value, apply the same hash function to the key and access that index

Example — simple hash function

hash(key) = key MOD 10
// key = 53 → 53 MOD 10 = 3 → store at index 3
// key = 27 → 27 MOD 10 = 7 → store at index 7

Collisions

A collision occurs when two different keys produce the same hash index. For example, keys 23 and 43 both hash to index 3 with key MOD 10. Collisions must be handled — one method is linear probing (check the next available slot).