Kerala Plus Two Computer Science (DHSE) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Structure member access

A structure variable accesses members with the dot operator, as in s.name. A pointer to a structure uses the arrow operator, p->name, which is shorthand for (*p).name.

Pointer dereference

The unary * operator accesses the value stored at the address held by a pointer. The pointer's declared type determines how many bytes are read and how they are interpreted.

new and delete

new allocates heap memory at run time and returns a pointer; delete releases it. For arrays use new[] and delete[]. Missing delete leaks memory; double delete is undefined behaviour.

Row-major address formula

In a two-dimensional array with C columns and element size S bytes, the address of a[i][j] equals base + (i * C + j) * S, since rows are stored consecutively.

Stack LIFO rule

A stack allows insertion and deletion only at one end, the top. The last element pushed is the first popped, so push and pop are both constant-time O(1) operations.

Circular queue condition

In a circular queue of capacity n, the next rear index is (rear + 1) % n. The queue is full when that index equals front; this reuses slots freed by dequeue.

Infix to postfix stack

Operators are held on a stack while converting infix to postfix. An operator is popped to output when one of higher or equal precedence arrives, respecting parentheses.

Binary search requirement

Binary search repeatedly halves a sorted array, giving O(log n) time. It requires random access by index, so it suits arrays but is impractical on linked lists.

Linked list node

A self-referential structure holding data and a pointer to the next node of the same type. Nodes need not be contiguous; the final node's next pointer is NULL.

Linked list deletion cost

Deleting a node at a known position is O(1): relink the predecessor to the successor, then free the node. Locating the position by traversal costs O(n).

Dangling pointer

A pointer that still holds the address of memory already freed by delete. Dereferencing it is undefined behaviour, so set the pointer to NULL after deletion.

Head and tail pointers

A singly linked list stores a head pointer to its first node. A queue also keeps a tail pointer so enqueue at the rear stays O(1) instead of O(n).

Encapsulation

Bundling data and the functions that operate on it inside a class, with private members hidden from outside code and reachable only through public member functions.

Run-time polymorphism

A base-class pointer or reference calls a virtual function, and the version belonging to the actual derived object executes. Resolution happens at run time through the vtable.

Abstract class

A class containing at least one pure virtual function, declared with = 0. It cannot be instantiated directly but serves as an interface for derived classes to implement.

Function overloading

Declaring several functions with the same name but different parameter lists in the same scope. The compiler chooses by argument count and types at compile time.

Copy constructor

A constructor taking a reference to the same class, used to initialise a new object from an existing one. It runs on pass-by-value and on initialisation from an object.

Constructor execution order

When a derived object is created, the base constructor runs first, then derived member initialisation in declaration order, then the derived constructor body.

Virtual destructor

Declaring the base destructor virtual ensures that deleting a derived object through a base pointer runs the derived destructor before the base destructor, avoiding leaks.

Primary key

An attribute or minimal set of attributes that uniquely identifies each tuple in a relation. It cannot contain NULL values and every relation has at most one.

WHERE versus HAVING

WHERE filters individual rows before grouping; HAVING filters groups after GROUP BY and aggregation, so aggregate conditions such as COUNT(*) > 3 belong in HAVING.

Referential integrity

A foreign key value must match an existing primary key value in the referenced relation, or be NULL. It prevents orphan rows and is enforced by the database.

CSS specificity order

When rules conflict, inline styles beat id selectors, which beat class selectors, which beat element selectors. Among equal specificity, the later rule wins.

CSS box model

Each element occupies content, then padding, border and margin. With box-sizing: border-box, the declared width includes padding and border but not margin.

Client-side validation

Checking form input in the browser with JavaScript gives fast feedback but can be bypassed, so the server must repeat every validation before storing or processing data.

PHP superglobal $_POST

An associative array holding form values submitted with method="post". The data travels in the request body rather than the URL, unlike values in $_GET.

PHP sessions versus cookies

Session data is stored on the server and linked to the client by a session ID; cookies are stored on the client and can be read or altered by the user.

SQL injection defence

Using prepared statements with bound parameters separates SQL code from user data, so input cannot alter the query structure. Escaping alone is weaker protection.

TCP versus UDP

TCP is connection-oriented and reliable, with acknowledgements, retransmission and ordered delivery. UDP is connectionless with no guarantees, suiting streaming and DNS queries.

DNS and DHCP roles

DNS maps human-readable domain names to IP addresses. DHCP automatically assigns IP addresses and related configuration to devices joining a network.

Cloud service models

IaaS supplies virtual machines and storage, PaaS supplies a managed runtime for deploying applications, and SaaS supplies finished applications accessed over the network.

Digital signature keys

The sender signs with a private key and any receiver verifies with the matching public key, proving origin and integrity and preventing the sender from denying the message.