NEB Class 12 Science Computer Science Question Paper 2077 Nepal

The if-else control structure is a conditional (decision-making) statement that executes one block of code when a condition is true and another block when it is false.

Syntax (C):

if (condition) {
    // statements executed when condition is true
} else {
    // statements executed when condition is false
}

Example:

if (marks >= 40)
    printf("Pass");
else
    printf("Fail");

Here, if marks is 40 or more it prints "Pass"; otherwise it prints "Fail".

Inheritance: An object-oriented feature by which a new class (derived/child class) acquires the properties (data members) and behaviours (member functions) of an existing class (base/parent class), promoting code reusability and establishing an "is-a" relationship.

Polymorphism: The ability of a single function, operator or object to take many forms / behave differently in different contexts (e.g. function overloading, operator overloading, virtual functions). It allows the same interface to invoke different implementations.

Function: A self-contained, named block of code that performs a specific task and can be called (invoked) whenever needed.

Advantages: (1) Code reusability — write once, call many times; (2) modularity — breaks a large program into manageable parts; (3) easier debugging and maintenance; (4) reduces program length and redundancy; (5) supports top-down design.

Library vs user-defined function:

Normalization: The process of organizing data in a database into tables and columns to reduce data redundancy and eliminate undesirable anomalies (insertion, update, deletion) by decomposing tables based on functional dependencies.

Advantages: reduces data redundancy; eliminates update/insert/delete anomalies; ensures data consistency and integrity; saves storage; makes the database easier to maintain.

Second Normal Form (2NF): A relation is in 2NF if it is in 1NF and every non-key attribute is fully functionally dependent on the whole primary key (no partial dependency). Example: in (StudentID, CourseID, CourseName) with composite key (StudentID, CourseID), CourseName depends only on CourseID (partial) → split into Enrolment(StudentID,CourseID) and Course(CourseID,CourseName).

Third Normal Form (3NF): A relation is in 3NF if it is in 2NF and has no transitive dependency (no non-key attribute depends on another non-key attribute). Example: Student(StudentID, DeptID, DeptName) — DeptName depends on DeptID (transitive) → split into Student(StudentID,DeptID) and Department(DeptID,DeptName).

The system analysis phase of the Software Development Life Cycle (SDLC) studies the existing system and the requirements of the proposed system in detail. Its main activities are: gathering requirements (interviews, questionnaires, observation, document review); analysing the current system and identifying problems and user needs; defining what the new system must do (functional and non-functional requirements); using tools such as DFDs, data dictionaries and use cases; and producing a requirement specification (SRS) that guides the design phase. It answers "what the system should do" rather than "how".

Database model: A logical structure / framework that defines how data is organised, stored, related and manipulated in a database (e.g. hierarchical, network, relational, object-oriented models).

Relational model: Proposed by E. F. Codd, it represents data as a collection of two-dimensional tables called relations. Each table has rows (tuples/records) and columns (attributes/fields); each row is uniquely identified by a primary key, and tables are linked using foreign keys. It supports operations through relational algebra/SQL, enforces data integrity (entity and referential integrity), and reduces redundancy. Example: a Student table related to a Department table via DeptID.

Bounded (guided) media carry signals along a physical, solid conductor or path; unbounded (unguided) media transmit signals through air/space without a physical conductor.

(a) AI (Artificial Intelligence): The branch of computer science concerned with building machines/programs that can perform tasks normally requiring human intelligence — learning, reasoning, problem-solving, perception, decision-making and language understanding. Applications include expert systems, robotics, natural language processing, machine learning and computer vision.

(b) Router: A network device that operates at the network layer and connects two or more different networks. It examines the destination IP address of packets and forwards them along the best available path using a routing table, enabling communication between networks (e.g. a LAN and the Internet).