# COMPUTER SCIENCE _868_

Document Sample

```					                                     COMPUTER SCIENCE (868)

CLASS XI (Scope)

operations for numbers in different bases.
a) The scope document contains details, explanatory
material and other information to help in teaching the     Introduce the positional system of representing
syllabus. It must be read in conjunction with the          numbers and the concept of a base. Discuss the
syllabus.                                                  conversion of representations between different bases
using English or pseudo code since students new to
b) The examples and problems given in this document
computing may be seeing algorithms for the first time.
are meant to be suggestive and indicative not
These algorithms are also good examples for defining
enumerative or exhaustive. That means that the
different functions in a class modelling numbers
student should typically know how to solve the
(when programming is discussed). For addition and
problems and be familiar with the examples
subtraction use the analogy with decimal numbers,
mentioned here but it does not mean that those are the
emphasize how carry works (this will be useful later
only problems or examples that will be examined in
the terminal examination.
Encodings
c) There is some information regarding environments
and software. This information again is in the nature      b) Binary encodings for integers and real numbers
of recommendations and is not mandatory. For the           using a finite number of bits (sign-magnitude, twos
programming part the recommendations are based on          complement, mantissa-exponent notation). Basic
an objects first approach to programming. Individual       operations on integers and floating point numbers.
teachers are perfectly free to use other software and      Limitations of finite representations.
environments that suit the way they wish to teach the
Signed, unsigned numbers, least and most significant
material.
bits. Sign-magnitude representation and its
d) The scope document follows the structure of the         shortcomings (two representations for 0, addition
syllabus. Each item of the syllabus is first reproduced    requires extra step); twos-complement representation.
in italics and the explanatory material then follows the   Operations (arithmetic, logical, shift), discuss the
reproduced item.                                           basic algorithms used for the arithmetic operations.
Floating point representation: normalized scientific
e) The syllabus per se does not assume any previous
notation, mantissa-exponent representation, binary
background as a pre-requisite. However, a majority of
point (discuss trade-off between size of mantissa and
students are likely to have done a computer
exponent). Single and double precision. Arithmetic
applications course at the class X level or may be
operations with floating point numbers. Properties of
otherwise familiar with programming. So, a balance
finite representation: overflow, underflow, lack of
has to be struck between the student without any
associativity (demonstrate this through actual
background and one with programming background.
programs).
Especially in sections B and C it is possible that the
‘fresh’ student may have to put in extra effort and the    c) Characters and their encodings (e.g. ASCII,
teacher may have to help such students with extra          Unicode).
assignments and explanations.
Discuss the limitations of the ASCII code in
SECTION A                             representing characters of other languages. Discuss
the Unicode representation for the local language.
Basic Computer hardware and software:                      Java uses Unicode, so strings in the local language can
Numbers                                                    be used (they can be displayed if fonts are available) –
a simple table lookup for local language equivalents
a) Representation of numbers in different bases and        for Latin (i.e. English) character strings should interest
interconversion between them (e.g. binary, octal,
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students. More details on Unicode are available at          f) Assembly language of 8085, simple assembly
www.unicode.org.                                            language programs, assembly process and assembler.
High level structure of computer                            Discussion of the assembly language should be done
along with the instruction set (previous section).
d) Block diagram of a computer system with details of
Emphasize how it is easier to program in assembly
i) function of each block and ii) interconnectivity and
language than in machine language. Assembly
data and control flow between the various blocks.
process: symbol table and its use in translating a
Develop the diagram by successive refinement of             program to machine language. Macros are not
blocks till all the following have been covered: ALU,       included.
RAM, cache, the buses (modern computers have
Propositional logic, hardware implementation,
multiple buses), disk (disk controller and what it
arithmetic operations
does), input/output ports (serial, parallel, USB,
network, modem, line-in, line-out etc.), devices that       g) Propositional logic, well formed formulae, truth
can be attached to these ports (e.g keyboard, mouse,        values and interpretation of well formed formulae,
monitor, CDROM, DVD, audio input/output devices,            truth tables.
printer, etc.). Clearly describe the connectivity and the
Propositional variables; the common logical
flow of data and control signals. .
connectives(∽ (not), ∧ (and), ∨ (or), ⇾ (implication),
Basic architecture of typical simple processor and
its assembly language                                       ⇿ (equivalence)); definition of a well-formed formula
e) Basic architecture of the 8085 microprocessor.           (wff); representation of simple word problems as wff
(this can be used for motivation); the values true and
false; interpretation of a wff; truth tables; satisfiable,
machine language programs using the different
unsatisfiable and valid formulae.
addressing modes, execution of machine language
programs, input and output.                                 h) Logic and hardware, basic gates (AND, NOT, OR)
and their universality, other gates (NAND, NOR,
The idea here is to discuss a concrete microprocessor
instead of an abstract computer thus giving students a
clearer understanding of how a typical computer             Show how the logic in g) can be realized in hardware
works. The aim is not to know all details of the 8085       in the form of gates. These gates can then be
microprocessor. The basic features that must be             combined to implement the basic operations for
covered are: i) Structure of memory; ii) registers - A-     arithmetic. Tie up with the arithmetic operations on
register (accumulator), general (B, C, D, E, H, L in 8-     integers discussed earlier in b).
bit individual and paired 16-bit modes), program
Memory
counter, stack pointer, flag; iii) addressing modes
(immediate, direct, register, register-indirect); iv)       i) Memory - construction of a memory bit using a flip-
Instruction set (data transfer, arithmetic, logical,        flop, D-flip-flop and its use in constructing registers.
conditional and transfer of control, input/output).
j) Memory organization and access; parity; memory
Interrupts are not included. Since many free
hierarchy - cache, primary memory, secondary
simulators are available the student should actually
memory.
write, run and observe what happens when a machine
language program runs. Example machine and                  The access time differences between the different
assembly language programs: evaluating simple               kinds of memory; size differences; locality of
expressions, adding a sequence of numbers, finding          reference and cache memory.
the minimum and/or maximum of a sequence of                 System and other software
numbers, using finding the minimum/maximum to do
sorting of a sequence of numbers. In particular,            k) Boot process. Operating system as resource
discuss how the stack can be used for calling and           manager, command processing, files, directories and
returning from subprograms. Emphasize how data and          file system. Commonly available programs (editors,
program look alike and depend on the interpretation         compilers, interpreters, word processors, spread
used.                                                       sheets etc.).
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Boot process step-by-step from power on till the             Primitive values, wrapper classes, types and
prompt. In OS discuss: i) all the resources (processor,      casting
memory, i/o) that need to be managed in a computer
c) Primitive values and types: int, short, long, float,
ii) what is meant by managing these resources.
double, boolean, char. Corresponding wrapper
Logical structure of data storage on disk using logical
classes for each primitive type. Class as type of the
disks, hierarchical directories and files. Distinguish
object. Class as mechanism for user defined types.
between interpreters and compilers. In particular
Changing types through user defined casting and
discuss the javac and java programs.
automatic type coercion for some primitive types.
Ideally, everything should be a class; primitive types
are defined for efficiency reasons; each primitive type
SECTION B                               has a corresponding wrapper class. Classes as user
defined types. In some cases types are changed by
The programming element in the syllabus is aimed at          automatic coercion or casting – e.g. mixed type
algorithmic problem solving and not merely rote              expressions. However, casting in general is not a good
learning of Java syntax. The Java version used should        idea and should be avoided, if possible.
be 1.5 or later. For programming, the students can use
any text editor and the javac and java programs or any       Variables, expressions
development environment: for example, BlueJ,                 d) Variables as names for values; expressions
Eclipse, NetBeans etc. BlueJ is strongly recommended         (arithmetic and logical) and their evaluation
for its simplicity, ease of use and because it is very       (operators, associativity, precedence). Assignment
well suited for an ‘objects first’ approach.                 operation; difference between left hand side and right
hand side of assignment.
Introduction to algorithmic problem solving using
Java                                                         Variables denote values; variables are already defined
as attributes in classes; variables have types that
Note that items a) to f) will get introduced almost          constrain the values it can denote. Difference between
simultaneously when classes and their definitions are        variables denoting primitive values and object values
introduced.                                                  – variables denoting objects are references to those
Objects                                                      objects. The assignment operator = is special. The
variable on the lhs of = denotes the memory location
a) Objects as data (attributes) + behaviour (methods         while the same variable on the rhs denotes the
or functions); object as an instance of a class.             contents of the location e.g. i=i+2.
Constructors.
Statements, scope
Difference between object and class should be made
very clear. BlueJ (www.bluej.org) and Greenfoot              e) Statements; conditional (if, if-then-else, switch-
(www.greenfoot.org) can be profitably used for this          break, ?: ternary operator), looping (for, while-do,
do-while, continue, break); grouping statements in
purpose. Constructor as a special kind of function; the
blocks, scope and visibility of variables.
new operator; multiple constructors with different
argument structures; constructor returns a reference to      Describe the semantics of the the conditional and
the object.                                                  looping statements in detail. Evaluation of the
condition in conditional statements (esp. difference
b) Analysis of some real world programming
between || and | and && and &). Emphasize fall
examples in terms of objects and classes.
through in switch statement. Many small examples
Use simple examples like a calculator, date, number          should be done to illustrate control structures. Printing
etc. to illustrate how they can be treated as objects that   different kinds of patterns for looping is instructive.
behave in certain well-defined ways and how the              When number of iterations are known in advance use
interface provides a way to access behaviour.                the for loop otherwise the while-do or do-while loop.
Illustrate behaviour changes by adding new functions,        Express one loop construct using the others. For e.g.:
deleting old functions or modifying existing functions.
for (<init>; <test>; <inc>) <stmt>; is equivalent to:

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Using while                                                   individual characters, various substring operations,
concatenation, replacement, index of operations).
<init>; while <test> {<stmt>; <inc> }
h) Basic concept of a virtual machine; Java virtual
Using do-while
machine; compilation and execution of Java programs
<init>; if !<test> do <stmt>; <inc> while <test>;             (the javac and java programs).
Nesting of blocks. Variables with block scope,                The JVM is a machine but built as a program and not
function scope, class scope. Visibility rules when            through hardware. Therefore it is called a virtual
variables with the same name are defined in different         machine. To run, JVM machine language programs
scopes.                                                       require an interpreter (the java program). The
Functions                                                     advantage is that such JVM machine language
programs (.class files) are portable and can run on any
f) Functions/methods (as abstractions for complex             machine that has the java program.
user defined operations on objects), functions as
mechanisms for side effects; formal arguments and             i) Compile time and run time errors; basic concept of
actual arguments in functions; different behaviour of         an exception, the Exception class, catch and throw.
primitive and object arguments. Static functions and          Differentiate between compile time and run time
variables. The this variable. Examples of algorithmic         errors. Run time errors crash the program. Recovery is
problem solving using functions (various number               possible by the use of exceptions. Explain how an
theoretic problems, finding roots of algebraic                exception object is created and passed up until a
equations).                                                   matching catch is found. This behaviour is different
Functions are like complex operations where the               from the one where a value is returned by a deeply
object is implicitly the first argument. Variable this        nested function call. It is enough to discuss the
denotes the current object. Functions typically return        Exception class. Sub-classes of Exception can be
values, they may also cause side-effects (e.g. change         discussed after inheritance has been done in class XII.
attribute values of objects) – typically functions that                            SECTION C
are only supposed to cause side-effects return void
Elementary data structures            and    associated
(e.g. Set functions). Java passes argument by value.
algorithms, basic input/ouput,
Illustrate the difference between primitive values and
object values as arguments (changes made inside               a) Class as a contract; separating implementation
functions persist after the call for object values). Static   from interface; encapsulation; private and public.
definitions as class variables and class functions
Class is the basic reusable unit. Its function prototypes
visible and shared by all instances. Need for static
(i.e. the interface) work as a visible contract with the
functions and variables. Introduce the main method –
outside world since others will use these functions in
needed to begin execution.
their programs. This leads to encapsulation (i.e. hiding
Arrays, strings                                               implementation information) which in turn leads to
the use of private and public for realizing
g) Structured data types – arrays (single and multi-
encapsulation.
dimensional), strings. Example algorithms that use
structured data types (e.g. searching, finding                b) Interfaces in Java; implementing interfaces through
maximum/minimum, sorting, solving systems of linear           a class; interfaces for user defined implementation of
char in string, etc.).
Motivation for interface: often when creating reusable
Storing many data elements of the same type requires          classes some parts of the exact implementation can
structured data types – like arrays. Access in arrays is      only be provided by the final end user. For example in
constant time and does not depend on the number of            a class that sorts records of different types the exact
elements. Structured data types can be defined by             comparison operation can only be provided by the end
classes – String. Introduce the Java library String class     user. Since only he/she knows which field(s) will be
and the basic operations on strings (accessing                used for doing the comparison and whether sorting

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should be in ascending or descending order be given       the File class, file input/output; input/output
by the user of the class.                                 exceptions. Tokens in an input stream, concept of
whitespace, extracting tokens from an input stream
Emphasize the difference between the Java language
(StringTokenizer class).
construct interface and the word interface often used
to describe the set of function prototypes of a class.    The Scanner class can be used for input of various
types of data (e.g. int, float, char etc.) from the
c) Basic data structures (stack, queue, dequeue);
standard input stream or a file input stream. The File
implementation directly through classes; definition
class is used model file objects in the underlying
through an interface and multiple implementations
system in an OS independent manner. Similarly, the
by implementing the interface. Basic algorithms using
Printer class handles output. Only basic input and
the above data structures.
output using these classes should be covered.
A data structure is a data collection with well           Discuss the concept of a token (a delimited continuous
defined operations and behaviour or properties.           stream of characters that is meaningful in the
The behaviour or properties can usually be                application program – e.g. words in a sentence where
expressed formally using equations or some kind           the delimiter is the blank character). This naturally
of logical formulae. Consider for e.g. a stack with       leads to the idea of delimiters and in particular
operations defined as follows:                            whitespace and user defined characters as delimiters.
As an example show how the StringTokenizer class
void push(Object o)                                       allows one to extract a sequence of tokens from a
Object pop()                                              string with user defined delimiters.
boolean isEmpty()                                         e) Concept of recursion, simple recursive functions
(e.g. factorial, GCD, binary search, conversion of
Object top()                                              representations of numbers between different bases).
Then, for example the LIFO property can be                Many problems can be solved very elegantly by
expressed by (assume s is a stack):                       observing that the solution can be composed of
solutions to ‘smaller’ versions of the same problem
if s.push(o); o1=pop() then o ≡ o1                        with the base version having a known simple solution.
Recursion can be initially motivated by using
What the rule says is: if o is pushed on the stack s      recursive equations to define certain functions. These
and then it is popped and o1 is the object obtained       definitions are fairly obvious and are easy to
then o, o1 are identical.                                 understand. The definitions can be directly converted
Another useful property is:                               to a program. Emphasize that any recursion must have
a base case. Otherwise, the computation can go into an
if s.isEmpty() == true then s.pop() = ERROR               infinite loop. Illustrate this by removing the base case
and running the program. Examples:
It says that popping an empty stack gives ERROR.
1) Definition of factorial:
Similarly, several other properties can also be
specified. It is important to emphasize the behavioural   factorial(0) = 1 //base case
rules or properties of a data structure since any
factorial(n) = n * factorial(n-1)
implementation must guarantee that the rules hold.
Definition of GCD:
Some simple algorithms that use the data structures:
gcd(m, n) =
i)   For stack: parentheses matching, tower of
Hanoi, nested function calls; solving a maze.    if (m==n) then n //base case
ii) For queue: scheduling processes, printers,        else if (m>n) then gcd(m-n, n)
jobs in a machine shop.                               else gcd(m, n-m)
d) Basic input/output using Scanner and Printer           Definition of Fibonacci numbers:
classes from JDK; files and their representation using
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fib(0) = 1 //base case                                     take on the average n/2 comparisons when the average
is taken over a statistically significant number of
fib(1) = 1 //base case
instances.
fib(n) = fib(n-1)+ fib(n-2)
v) Comparisons are normally made for large values of
The tower of Hanoi is a very good example of how           the input size. This means that the dominant term in
recursion gives a very simple and elegant solution         the function is the important term. For example if we
where as non-recursive solutions are quite complex.        are looking at bubble sort and see that time taken can
Discuss the use of a stack to keep track of function       be estimated as: a*n2 +b*n + c where n is the number
calls. The stack can also be used to solve the tower of    of elements to be sorted and a, b, c are constants then
Hanoi problem non-recursively.                             for large n the dominant term is clearly n2 and we can
f) Concrete computational complexity; concept of           in effect ignore the other two terms.
input size; estimating complexity in terms of functions;   Implementation of algorithms to solve problems
importance of dominant term; best, average and worst
case.                                                      The students are required to do lab assignments in the
Points to be given particular emphasis:                    computer lab concurrently with the lectures.
Programming assignments should be done such that
i) Algorithms are usually compared along two               each major topic is covered in at least one assignment.
dimensions – amount of space (that is memory) used         Assignment problems should be designed so that they
and the time taken. Of the two the time taken is           are non-trivial and make the student do algorithm
usually considered the more important. The                 design, address correctness issues, implement and
motivation to study time complexity is to compare          execute the algorithm in Java and debug where
different algorithms and use the one that is the most      necessary. Some sample problems are given in the
efficient in a particular situation.                       scope document.
ii) Actual run time on a particular computer is not a
good basis for comparison since it depends heavily on      Social context of computing and ethical issues
the speed of the computer, the total amount of RAM         g) Intellectual property and corresponding laws and
in the computer, the OS running on the system and the      rights, software as intellectual property.
quality of the compiler used. So we need a more
abstract way to compare the time complexity of             h) Software copyright and patents and the difference
algorithms.                                                between the two; trademarks; software licensing and
piracy.
iii) This is done by trying to approximate the number
of operations done by each algorithm as a function of      i) Free software foundation and its position on
the size of the input. In most programs the loops are      software, open source software, various types of
important in deciding the complexity. For example in       licensing (e.g. GPL, BSD).
bubble sort there are two nested loops and in the worst
j) Privacy, email etiquette, spam, security issues,
case the time taken will be proportional to n(n-1)
phising.
where n is the number of elements to be sorted.
Similarly, in linear search in the worst case the target   Social impact and ethical issues should be discussed
has to be compared with all the elements so time taken     and debated in class. The important thing is for
will be proportional to n where n is the number of         students to realise that these are complex issues and
elements in the search set.                                their are multiple points of view on many of them and
iv) In most algorithms the actual complexity for a         there is no single ‘correct’ or ‘right’ view.
particular input can vary. For example in search the         (Questions on social context of computing and ethical
number of comparisons can vary from 1 to n. This             issues should be short answer questions and should be
means we need to study the best, worst and average           asked only in Part I).
cases. Comparisons are usually made taking the worst
case. Average cases are harder to estimate since it
depends on how the data is distributed. For example in
search, if the elements are uniformly distributed it will
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PAPER II - PRACTICAL                          Continuous Evaluation
Programming assignments in Java throughout the year
This paper will be evaluated internally by the school.
The evaluation shall consist of a 3-hour practical                                                          20 marks
examination at the end of the year and evaluation of
Terminal Evaluation
all assignments done throughout the year.
Java solution to programming problem            - 60 marks
The terminal examination of three hours duration shall
consist of three programming problems from which a          (Marks should be given for choice of algorithm and
candidate has to attempt any one. In each problem a         implementation strategy, documentation, correct output
candidate will be required to write and execute a Java      on known inputs mentioned in the question paper,
program on seen and unseen inputs. The program              correct output for unknown inputs available only to the
should be sufficiently documented so that the               examiner.)
algorithm and the development process is clear from
reading the program.                                        Viva-Voce (based on the programming problem chosen
by the student)                         - 20 marks
Teachers should maintain a record of all the
assignments done as part of the practical work through      (Viva-voce includes questions on the following aspects
the year and give it due credit at the time of              of the problem attempted by the student: the algorithm
cumulative evaluation at the end of the year.               and     implementation      strategy,    documentation,
Marks (out of a total of 100) will be distributed as        correctness, alternative algorithms or implementations.
given below:                                                Questions should be confined largely to the problem
the student has attempted.)
CLASS XII (Scope)
There will be two papers in the subject:                    formulae. Equivalence laws and their use in
simplifying wffs.
Paper I: Theory-         3 hours        …100 marks
Propositional variables; the common logical
Paper II: Practical-     3 hours        …100 marks
connectives(∽ (not), ∧ (and), ∨ (or), ⇒ (implication),
PAPER I-THEORY                             ⇔ (biconditional); definition of a well-formed formula
Paper 1 shall be of 3 hours duration and be divided         (wff); representation of simple word problems as wff
into two parts.                                             (this can be used for motivation); the values true and
false; interpretation of a wff; truth tables; satisfiable,
Part I (30 marks): This part will consist of                unsatisfiable and valid formulae.
knowledge, application and skills relating to the entire    Equivalence laws: commutativity of ∧, ∨; associativity
syllabus.
of ∧,∨; distributivity; de Morgan’s laws; law of
Part II (70 marks): This part will be divided into
implication (p ⇒ q ≡ ∽p ∨ q); law of biconditional ((p
three Sections, A, B and C. Candidates are required to
answer three questions out of four from Section A and       ⇔ q) ≡ (p ⇒ q) ∧ (q ⇒ p)); identity (p ≡ p); law of
two questions out of three in each of the sections B
and C. Each question in this part shall carry 10            negation ( ∽(∽p) ≡ p); law of excluded middle (p ∨ ∽p
marks.                                                      ≡ true); law of contradiction(p ∧∽p ≡ false);
SECTION A                            simplification rules for ∧, ∨.
Boolean Algebra
p∨p≡p                        p∧p≡p
a) Propositional logic, well formed formulae, truth
values and interpretation of well formed formulae           p ∨ true ≡ true              p ∧ true ≡ p
(wff), truth tables, satisfiable, unsatisfiable and valid   p ∨ false ≡ p                p ∧ false ≡ false
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p ∨ (p ∧ q) ≡ p                p ∧ (p ∨ q) ≡ p             and because it is very well suited for an ‘objects first’
approach.

The equivalence rules can be used to simplify              Programming in Java (Review of class XI sections
propositional wffs, for example:                           B and C)

1) (p ⇒ q) ∧ (p ⇒ r) to p ⇒ (q ∧ r)                        Note that items a) to f) will get introduced almost
simultaneously when classes and their definitions are
2) ((p ⇒ q) ∧ p) ⇒ q to true                               introduced.
etc.                                                       Objects
b) Binary valued quantities; basic postulates of           a) Objects as data (attributes) + behaviour (methods
Boolean algebra; operations AND, OR and NOT;               or functions); object as an instance of a class.
truth tables.                                              Constructors.
c) Basic theorems of Boolean algebra (e.g. Duality,        Difference between object and class should be made
idempotence,         commutativity,       associativity,   very clear. BlueJ (www.bluej.org) and Greenfoot
distributivity, operations with 0 and 1, complements,      (www.greenfoot.org) can be profitably used for this
absorption, involution); De Morgan’s theorem and its       purpose. Constructor as a special kind of function; the
applications; reducing Boolean expressions to sum of       new operator; multiple constructors with different
products and product of sums forms; Karnaugh maps          argument structures; constructor returns a reference to
(up to four variables).                                    the object.
b) Analysis of some real world programming
Verify the laws of boolean algebra using truth tables.
examples in terms of objects and classes.
Inputs, outputs for circuits like half and full adders,
majority circuit etc., SOP representation; reduction       Use simple examples like a calculator, date, number
using Karnaugh maps and boolean algebra.                   etc. to illustrate how they can be treated as objects that
behave in certain well-defined ways and how the
Computer Hardware                                          interface provides a way to access behaviour.
d) Elementary logic gates (NOT, AND, OR, NAND,             Illustrate behaviour changes by adding new functions,
NOR, XOR, XNOR) and their use in circuits.                 deleting old functions or modifying existing functions.

e) Applications of Boolean algebra and logic gates to      Primitive values, wrapper classes, types and
multiplexers, NAND, NOR as universal gates.                c) Primitive values and types: int, short, long, float,
Show the correspondence between boolean functions          double, boolean, char. Corresponding wrapper
and the corresponding switching circuits or gates.         classes for each primitive type. Class as type of the
Show that NAND and NOR gates are universal by              object. Class as mechanism for user defined types.
converting some circuits to purely NAND or NOR             Changing types through user defined casting and
gates.                                                     automatic type coercion for some primitive types.
Ideally, everything should be a class; primitive types
SECTION B                             are defined for efficiency reasons; each primitive type
The programming element in the syllabus (sections B        has a corresponding wrapper class. Classes as user
and C) is aimed at algorithmic problem solving and         defined types. In some cases types are changed by
not merely rote learning of Java syntax. The Java          automatic coercion or casting – e.g. mixed type
version used should be 1.5 or later. For programming,      expressions. However, casting in general is not a good
the students can use any text editor and the javac and     idea and should be avoided, if possible.
java programs or any development environment: for          Variables, expressions
example, BlueJ, Eclipse, NetBeans etc. BlueJ is
strongly recommended for its simplicity, ease of use       d) Variables as names for values; expressions
(arithmetic and logical) and their evaluation
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(operators, associativity, precedence). Assignment          theoretic problems, finding roots of algebraic
operation; difference between left hand side and right      equations).
hand side of assignment.
Functions are like complex operations where the
Variables denote values; variables are already defined      object is implicitly the first argument. Variable this
as attributes in classes; variables have types that         denotes the current object. Functions typically return
constrain the values it can denote. Difference between      values, they may also cause side-effects (e.g. change
variables denoting primitive values and object values       attribute values of objects) – typically functions that
– variables denoting objects are references to those        are only supposed to cause side-effects return void
objects. The assignment operator = is special. The          (e.g. Set functions). Java passes argument by value.
variable on the lhs of = denotes the memory location        Illustrate the difference between primitive values and
while the same variable on the rhs denotes the              object values as arguments (changes made inside
contents of the location e.g. i=i+2.                        functions persist after the call for object values). Static
definitions as class variables and class functions
Statements, scope
visible and shared by all instances. Need for static
e) Statements; conditional (if, if-then-else, switch-       functions and variables. Introduce the main method –
break, ?: ternary operator), looping (for, while-do,        needed to begin execution.
do-while, continue, break); grouping statements in
Arrays, strings
blocks, scope and visibility of variables.
g) Structured data types – arrays (single and multi-
Describe the semantics of the the conditional and
dimensional), strings. Example algorithms that use
looping statements in detail. Evaluation of the
structured data types (e.g. searching, finding
condition in conditional statements (esp. difference
maximum/minimum, sorting, solving systems of linear
between || and | and && and &). Emphasize fall
through in switch statement. Many small examples
char in string, etc.).
should be done to illustrate control structures. Printing
different kinds of patterns for looping is instructive.     Storing many data elements of the same type requires
When number of iterations are known in advance use          structured data types – like arrays. Access in arrays is
the for loop otherwise the while-do or do-while loop.       constant time and does not depend on the number of
Express one loop construct using the others. For e.g.:      elements. Structured data types can be defined by
classes – String. Introduce the Java library String class
for (<init>; <test>; <inc>) <stmt>; is equivalent to:
and the basic operations on strings (accessing
Using while                                                 individual characters, various substring operations,
<init>; while <test> {<stmt>; <inc> }                       concatenation, replacement, index of operations).

Using do-while                                              h) Basic concept of a virtual machine; Java virtual
machine; compilation and execution of Java programs
<init>; if !<test> do <stmt>; <inc> while <test>;           (the javac and java programs).
Nesting of blocks. Variables with block scope,              The JVM is a machine but built as a program and not
function scope, class scope. Visibility rules when          through hardware. Therefore it is called a virtual
variables with the same name are defined in different       machine. To run, JVM machine language programs
scopes.                                                     require an interpreter (the java program). The
Functions                                                   advantage is that such JVM machine language
programs (.class files) are portable and can run on any
f) Functions/methods (as abstractions for complex           machine that has the java program.
user defined operations on objects), functions as
mechanisms for side effects; formal arguments and           i) Compile time and run time errors; basic concept of
actual arguments in functions; different behaviour of       an exception, the Exception class, catch and throw.
primitive and object arguments. Static functions and        Differentiate between compile time and run time
variables. The this variable. Examples of algorithmic       errors. Run time errors crash the program. Recovery is
problem solving using functions (various number             possible by the use of exceptions. Explain how an
exception object is created and passed up until a
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matching catch is found. This behaviour is different        whitespace and user defined characters as delimiters.
from the one where a value is returned by a deeply          As an example show how the StringTokenizer class
nested function call. It is enough to discuss the           allows one to extract a sequence of tokens from a
Exception class. Sub-classes of Exception can be            string with user defined delimiters.
discussed after inheritance has been done in class XII.
m) Concept of recursion, simple recursive functions
j) Class as a contract; separating implementation           (e.g. factorial, GCD, binary search, conversion of
from interface; encapsulation; private and public.          representations of numbers between different bases).
Class is the basic reusable unit. Its function prototypes   Many problems can be solved very elegantly by
(i.e. the interface) work as a visible contract with the    observing that the solution can be composed of
outside world since others will use these functions in      solutions to ‘smaller’ versions of the same problem
their programs. This leads to encapsulation (i.e. hiding    with the base version having a known simple solution.
implementation information) which in turn leads to          Recursion can be initially motivated by using
the use of private and public for realizing                 recursive equations to define certain functions. These
encapsulation.                                              definitions are fairly obvious and are easy to
understand. The definitions can be directly converted
k) Interfaces in Java; implementing interfaces through
to a program. Emphasize that any recursion must have
a class; interfaces for user defined implementation of
a base case. Otherwise, the computation can go into an
behaviour .
infinite loop. Illustrate this by removing the base case
Motivation for interface: often when creating reusable      and running the program. Examples:
classes some parts of the exact implementation can
1) Definition of factorial:
only be provided by the final end user. For example in
a class that sorts records of different types the exact     factorial(0) = 1 //base case
comparison operation can only be provided by the end
factorial(n) = n * factorial(n-1)
user. Since only he/she knows which field(s) will be
used for doing the comparison and whether sorting           2) Definition of GCD:
should be in ascending or descending order be given         gcd(m, n) =
by the user of the class.
if (m==n) then n //base case
Emphasize the difference between the Java language
construct interface and the word interface often used       else if (m>n) then gcd(m-n, n)
to describe the set of function prototypes of a class.          else gcd(m, n-m)
l) Basic input/output using Scanner and Printer             3) Definition of Fibonacci numbers:
classes from JDK; files and their representation using
the File class, file input/output; input/output             fib(0) = 1 //base case
exceptions. Tokens in an input stream, concept of           fib(1) = 1 //base case
whitespace, extracting tokens from an input stream
(StringTokenizer class).                                    fib(n) = fib(n-1)+ fib(n-2)
The Scanner class can be used for input of various          The tower of Hanoi is a very good example of how
types of data (e.g. int, float, char etc.) from the         recursion gives a very simple and elegant solution
standard input stream or a file input stream. The File      where as non-recursive solutions are quite complex.
class is used model file objects in the underlying          Discuss the use of a stack to keep track of function
system in an OS independent manner. Similarly, the          calls. A stack can also be used to solve the tower of
Printer class handles output. Only basic input and          Hanoi problem non-recursively.
output using these classes should be covered.
Discuss the concept of a token (a delimited continuous                           SECTION C
stream of characters that is meaningful in the
application program – e.g. words in a sentence where        Inheritance, polymorphism,          data    structures,
the delimiter is the blank character). This naturally       computational complexity
leads to the idea of delimiters and in particular           Inheritance and polymorphism
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a) Inheritance; base and derived classes; member          void push(Object o)
access in derived classes; redefinition of variables
and functions in subclasses; abstract classes; class      Object pop()
Object; protected visibility. Subclass polymorphism       boolean isEmpty()
and dynamic binding.
Object top()
Emphasize the following:
Then, for example the LIFO property can be
- inheritance as a mechanism to reuse a class by
expressed by (assume s is a stack):
extending it.
- inheritance should not normally be used just to reuse   if s.push(o); o1=pop() then o ≡ o1
some functions defined in a class but only when there
is a genuine specialization (or subclass) relationship    What the rule says is: if o is pushed on the stack s
between objects of the base class and that of the         and then it is popped and o1 is the object obtained
derived class.                                            then o, o1 are identical.
- Allows one to implement operations at the highest       Another useful property is:
relevant level of abstraction.
if s.isEmpty() == true then s.pop() = ERROR
- Freezes the interface in the form of abstract classes
It says that popping an empty stack gives ERROR.
with abstract functions that can be extended by the
concrete implementing classes. For example, an            Similarly, several other properties can also be
abstract class Shape can have an abstract function        specified. It is important to emphasize the behavioural
draw that is implemented differently in the sub-classes   rules or properties of a data structure since any
like Circle, Quadrilateral etc.                           implementation must guarantee that the rules hold.
- how the exact function call at run time depends on      Some simple algorithms that use the data structures:
the type of the object referenced by the variable. This
i) For stack: parentheses matching, tower of Hanoi,
gives sub-class polymorphism. For example in the
nested function calls; solving a maze.
code fragment:
ii) For queue: scheduling processes, printers, jobs in a
machine shop.
s1.draw(); //the draw is the draw in Circle
c) Recursive data structures: singly and doubly linked
s2.draw(); //the draw is the draw in Quadrilateral        lists, binary trees, tree traversals, binary search tree.
Algorithms using these data structures (merge sort
the two draw function invocations on s1, s2 invoke
and quick sort, searching.
different draw functions depending on the type of
objects referenced by s1 and s2 respectively.             Data structures should be defined as abstract data
types with a well defined interface (it is instructive to
Data structures
define them using the Java interface construct) – see
b) Basic data structures (stack, queue, dequeue);         the comments in b) above. Emphasize that algorithms
implementation directly through classes; definition       for recursive data structures are themselves recursive
through an interface and multiple implementations         and that algorithms are usually the simplest and most
by implementing the interface. Basic algorithms using     elegant. The following should be covered for each
the above data structures.                                data structure:
A data structure is a data collection with well           Lists: insertion, deletion, reversal, appending two lists,
defined operations and behaviour or properties.           extracting an element or a sublist, checking
The behaviour or properties can usually be                emptiness. Searching, sorting (by quicksort and
expressed formally using equations or some kind           mergesort algorithms), binary search in a sorted list.
of logical formulae. Consider for e.g. a stack with       Binary trees: apart from the definition the following
operations defined as follows:                            concepts should be covered external and internal
nodes, height, completeness, balancing, Traversals
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(pre, post and in-order). Implementation using arrays       is taken over a statistically significant number of
Binary search tree: insertion, deletion, search.            v) Comparisons are normally made for large values of
the input size. This means that the dominant term in
Complexity and big O notation
the function is the important term. For example if we
d) Concrete computational complexity; concept of            are looking at bubble sort and see that time taken can
input size; estimating complexity in terms of functions;    be estimated as: a*n2 +b*n + c where n is the number
importance of dominant term; best, average and worst        of elements to be sorted and a, b, c are constants then
case. Big O notation for computational complexity;          for large n the dominant term is clearly n2 and we can,
analysis of complexity of example algorithms using          in effect, ignore the other two terms.
the big O notation (e.g. Various searching and sorting
All the above motivates the big O notation. Let f(n),
algorithms, algorithm for solution of linear equations
g(n) be positive functions, then f(n) is said to be
etc.).
O(g(n)) if there exists constants c, n0 such that f(x)≤
Points to be given particular emphasis:
c*g(n) whenever n>n0. What this means is that g(n)
i) Algorithms are usually compared along two                asymptotically dominates f(n). Expressing time
dimensions – amount of space (that is memory) used          complexity using the big O notation gives us an
and the time taken. Of the two the time taken is            abstract basis for comparison and frees us from
usually considered the more important. The                  bothering about constants. So the estimated time
motivation to study time complexity is to compare           complexity a*n2+b*n+c is O(n2).
different algorithms and use the one that is the most
Analyse the big O complexity of the algorithms
efficient in a particular situation.
pertaining to the data structures in parts b) and c)
ii) Actual run time on a particular computer is not a       above.
good basis for comparison since it depends heavily on
the speed of the computer, the total amount of RAM          Implementation of algorithms to solve problems
in the computer, the OS running on the system and the       The students are required to do lab assignments in the
quality of the compiler used. So we need a more             computer lab concurrently with the lectures.
abstract way to compare the time complexity of              Programming assignments should be done such that
algorithms.                                                 each major topic is covered in at least one assignment.
iii) This is done by trying to approximate the number       Assignment problems should be designed so that they
of operations done by each algorithm as a function of       are non-trivial and make the student do algorithm
the size of the input. In most programs the loops are       design, address correctness issues, implement and
important in deciding the complexity. For example in        execute the algorithm in Java and debug where
bubble sort there are two nested loops and in the worst     necessary.
case the time taken will be proportional to n(n-1)
where n is the number of elements to be sorted.
Similarly, in linear search in the worst case the target
has to be compared with all the elements so time taken                   PAPER II - PRACTICAL
will be proportional to n where n is the number of
elements in the search set.                                 This paper of three hours duration will be evaluated
by the teacher and a Visiting Examiner appointed
iv) In most algorithms the actual complexity for a          locally and approved by the Council.
particular input can vary. For example in search the
number of comparisons can vary from 1 to n. This            The paper shall consist of three programming
means we need to study the best, worst and average          problems from which a candidate has to attempt any
cases. Comparisons are usually made taking the worst        one. In each problem a candidate will be required to
case. Average cases are harder to estimate since it         write and execute a Java program on seen and unseen
depends on how the data is distributed. For example in      inputs. The program should be sufficiently
search, if the elements are uniformly distributed it will   documented so that the algorithm, representation and
take on the average n/2 comparisons when the average
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development process is clear from reading the                A white board with white board markers should
program.                                                      be available.
Marks (out of a total of 100) should be distributed as       A fully equipped Computer Laboratory that
given below:                                                  allows one computer per student.
Continuous Evaluation                                        Internet connection for accessing the World Wide
Candidates will be required to submit a work file             Web and email facility.
containing the practical work related to programming         The computers should have a minimum of 256
assignments done during the year.
MB (512MB preferred) RAM and a PIII or higher
Programming assignments done throughout the year              processor. The basic requirement is that it should
(Internal evaluation)                  - 10 marks             run the operating system and Java programming
Programming assignments done throughout the year              system (Java compiler, Java runtime environment,
(Visiting Examiner)                     - 10 marks            Java development environment) at acceptable
speeds.
Terminal Evaluation
Solution to programming problem on the computer              Good Quality printers.
 60 marks        Software:
(Marks should be given for choice of algorithm and
   Any suitable Operating System can be used.
implementation strategy, documentation, correct output
on known inputs mentioned in the question paper,             JDK 1.5 or later.
correct output for unknown inputs available only to the
   Documentation for the JDK version being used.
examiner.)
Viva-voce                                   - 20 marks       A suitable text editor. A development
environment with a debugger is preferred (e.g.
(Viva-voce includes questions on the following                BlueJ, Eclipse, NetBeans). BlueJ is recommended
aspects of the problem attempted by the student: the          for its ease of use and simplicity.
algorithm       and      implementation       strategy,
documentation, correctness, alternative algorithms or
implementations. Questions should be confined
largely to the problem the student has attempted.)

EQUIPMENT
There should be enough computers to provide for a
teaching schedule where at least three-fourths of the
time available is used for programming.
Schools should have equipment/platforms such that all
the software required for practical work runs properly,
i.e. it should run at acceptable speeds.
Since hardware and software evolve and change very
rapidly, the schools may have to upgrade them as
required.    Following    are  the   recommended
specifications as of now:
The Facilities:
   A lecture cum demonstration room with a
MULTIMEDIA PROJECTOR/ an LCD and
O.H.P. attached to the computer.
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