UGC NET Computer Science Programming Languages and Computer Graphics Syllabus

Define the four pillars of Object-Oriented Programming.

1) Encapsulation (binding data and methods, hiding internals), 2) Abstraction (exposing essential features only), 3) Inheritance (deriving new classes from existing ones), 4) Polymorphism (one interface, many forms).

What is the difference between a class and an object?

A class is a blueprint/template defining attributes and behaviors. An object is a runtime instance of a class with its own state; creating an object is called instantiation.

What is an abstract class in C++, and how is one created?

An abstract class cannot be instantiated and serves as a base for derived classes. In C++ it is created by declaring at least one pure virtual function (e.g., virtual void f() = 0;).

Differentiate compile-time polymorphism from run-time polymorphism in C++.

Compile-time (static) polymorphism is achieved via function/operator overloading and templates, resolved at compile time. Run-time (dynamic) polymorphism is achieved via virtual functions and inheritance, resolved at run time through the vtable.

What is a virtual function in C++ and why is it used?

A virtual function is a member function declared with the 'virtual' keyword in a base class, allowing it to be overridden in derived classes. It enables run-time polymorphism via dynamic dispatch using the object's actual type.

What is the difference between a constructor and a destructor in C++?

A constructor has the class name, no return type, runs automatically on object creation to initialize it, and can be overloaded. A destructor (~ClassName) runs automatically on object destruction to release resources, takes no arguments, and cannot be overloaded.

What is function overloading in C++ and on what basis are overloaded functions distinguished?

Function overloading allows multiple functions with the same name in the same scope, distinguished by their parameter list (number, types, or order of parameters). Return type alone cannot distinguish overloads.

List the main types of inheritance supported in C++.

Single, Multiple, Multilevel, Hierarchical, and Hybrid inheritance. Multiple/hybrid inheritance can cause the diamond problem, resolved using virtual base classes.

What is a template in C++ and what are its two kinds?

A template enables generic programming by writing code parameterized over types. The two kinds are function templates (generic functions) and class templates (generic classes), e.g., template<class T>.

In C++ exception handling, what is the purpose of try, throw, and catch?

try encloses code that may raise an exception; throw signals/raises an exception; catch handles a thrown exception of a matching type. This separates error-handling code from normal flow.

What is the difference between the C++ stream operators << and >> with cin/cout?

cout << uses the insertion operator to write/output data to a stream. cin >> uses the extraction operator to read/input data from a stream. They are overloaded for built-in types.

In C++ multifile programs, what is the purpose of the 'extern' keyword?

'extern' declares that a variable or function is defined in another file/translation unit, providing a reference without allocating storage, enabling sharing of globals across multiple files.

What does HTML stand for, and what is the difference between HTML and DHTML?

HTML = HyperText Markup Language, used to structure static web pages. DHTML (Dynamic HTML) is not a language but a combination of HTML, CSS, and client-side scripting (JavaScript) plus the DOM to create interactive, dynamic pages.

What is the primary difference between HTML and XML?

HTML has predefined tags and focuses on displaying/formatting data. XML (eXtensible Markup Language) lets users define custom tags and focuses on storing and transporting data; it is case-sensitive and requires well-formed, properly closed tags.

What is the difference between a Java Applet and a Java Servlet?

An applet is a client-side Java program that runs in a browser/JVM on the client. A servlet is a server-side Java program that runs on a web server to handle requests and generate dynamic responses (e.g., HTML).

What is the difference between client-side scripting and server-side scripting?

Client-side scripting (e.g., JavaScript) runs in the user's browser to handle interactivity and validation. Server-side scripting (e.g., servlets, PHP) runs on the server to process requests, access databases, and generate dynamic content.

What is the difference between a Raster-Scan and a Random-Scan (vector) display system?

Raster-scan stores the image as a pixel array (frame buffer) and refreshes line-by-line; suited for realistic shaded images. Random-scan draws lines directly point-to-point from a display file; gives high-resolution smooth lines but cannot shade well.

In a raster display, what is the frame buffer and how is color depth related to it?

The frame buffer (refresh buffer) is the memory holding intensity/color values for every pixel. Color depth = bits per pixel; n bits give 2^n colors (e.g., 8 bits = 256 colors). Total memory = width x height x bits-per-pixel.

Define refresh rate and aspect ratio for a video display device.

Refresh rate is how many times per second the screen is redrawn (e.g., 60 Hz) to avoid flicker. Aspect ratio is the ratio of horizontal to vertical dimensions/pixels of the display (e.g., 4:3, 16:9).

What is interlacing in raster-scan displays?

Interlacing refreshes odd-numbered scan lines in one pass and even-numbered lines in the next, displaying all even/odd lines alternately. It allows showing the whole image at half the bandwidth/refresh, reducing flicker on slower systems.

State the basic Digital Differential Analyzer (DDA) line-drawing algorithm steps.

Compute dx, dy; set steps = max(|dx|,|dy|); xinc = dx/steps, yinc = dy/steps; start at (x1,y1); repeatedly add increments and plot the rounded point. DDA uses floating-point arithmetic, causing rounding and accumulation errors.

What advantage does Bresenham's line algorithm have over the DDA algorithm?

Bresenham's algorithm uses only integer addition, subtraction, and bit shifting (no floating point or rounding), making it faster and free of accumulated rounding error compared to DDA.

In Bresenham's line algorithm (slope 0<m<1), what is the initial decision parameter?

p0 = 2*dy - dx, where dx = x2-x1 and dy = y2-y1. If pk < 0, plot (x+1, y) and pk+1 = pk + 2*dy; else plot (x+1, y+1) and pk+1 = pk + 2*dy - 2*dx.

In the midpoint circle algorithm, what is the initial decision parameter for a circle of radius r centered at origin?

p0 = 1 - r (or 5/4 - r, approximated to 1 - r). Starting at (0, r): if pk < 0, next point (xk+1, yk) with pk+1 = pk + 2xk+1 + 1; else (xk+1, yk-1) with pk+1 = pk + 2xk+1 + 1 - 2yk+1.

What symmetry does the midpoint circle algorithm exploit to reduce computation?

Eight-way (octant) symmetry: it computes points only for one 45-degree octant and reflects them to the other seven octants, e.g., from (x,y) it plots (±x,±y) and (±y,±x).

On what principle does the Scan-Line Polygon Fill algorithm operate?

For each scan line crossing the polygon, it finds intersections with polygon edges, sorts them by x, and fills pixels in pairs (between odd-even pairs of intersections), using an edge table and active edge list.

What is the difference between the Boundary-Fill and Flood-Fill algorithms?

Boundary-fill fills outward from a seed until it reaches a specified boundary color. Flood-fill replaces all connected pixels of a specific interior (old) color with a new color, regardless of a single boundary color; useful when boundaries have multiple colors.

Why are homogeneous coordinates used in 2-D geometric transformations?

Homogeneous coordinates represent a 2-D point (x,y) as (x,y,1), allowing translation, rotation, and scaling to all be expressed as 3x3 matrix multiplications. This lets multiple transformations be combined (composed) into a single matrix.

Give the 2-D transformation matrices (homogeneous) for translation and scaling.

Translation by (tx,ty): [[1,0,tx],[0,1,ty],[0,0,1]]. Scaling by (sx,sy): [[sx,0,0],[0,sy,0],[0,0,1]]. Applied to point [x,y,1]^T.

What is the 2-D rotation transformation matrix for an angle θ about the origin?

[[cosθ, -sinθ, 0], [sinθ, cosθ, 0], [0, 0, 1]], so x' = x cosθ - y sinθ and y' = x sinθ + y cosθ (counterclockwise about the origin).

Name common methods of 3-D object representation in computer graphics.

Boundary representations (B-reps) such as polygon meshes and wireframes; space-partitioning representations such as octrees; plus constructive solid geometry (CSG), sweep representations, and parametric/spline surfaces (e.g., Bezier, B-spline).