Download Lab Session-II CS121 Summer-I 1999

Pre-Exam Lecture
 Final Examination is scheduled on Monday
December 18th at 1:30PM in class
 There are 8 questions with or without subparts and the exam carries 30 Marks
 Let us look at the topics included in the
exam
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Topics in Exam
 *Algorithms
 Architecture of the Processor (ALU, Data
Path and Memory Interface)
 Operating Systems
 Searching and Sorting a List
 *Binary and Hex Numbers
 Digital Logic
 2GL, 3GL and 4GL concepts
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Topics in Exam
 Software Engineering Basic Concepts
 *Waterfall model and spiral model
 Arrays, Contiguous and Linked Lists,
Stacks and Binary Search Tree
 Database Systems (Network and Relational)
 Symmetric Key Encryption and publicprivate key encryption
 Ethics in Computing
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*Algorithms
 An algorithm is a step by step method to
solve a problem with a definite reachable
termination state
 Most algorithms can be developed by
following the instructions below:
– Read the problem statement and rewrite it in
your own words to make it simple
– Consider nouns used and identify the data items
– Consider the verbs used and identify the actions4
to be taken
*Algorithms
– Write the initial algorithm in terms of WHAT is
to be accomplished
– Refine each step of the initial algorithm to
include the details of HOW the step would be
accomplished
 In the exam, expect a question that asks you
to develop an algorithm for solving a given
problem on computer
 DO NOT WRITE A C++ PROGRAM IN
YOUR ANSWER
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Architecture
 It is important to understand how the
processor executes a program
 The processor obtains instructions one by
one from memory through a “bus” using PC
 Instructions are loaded in IR(instruction
register) in the control unit
 Operands are brought into the data path
 ALU operates on the operands and result is
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sent to memory or held in registers
Operating Systems
 Operating systems are programs that run the
computers
 Distinguish between batch and interactive
systems
 Think about the “time-sharing” systems
 Think about Windows, UNIX and other
operating systems
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Searching and Sorting a List
 We looked at the while statement that is
needed in searching and sorting operations
 while loop is recommended when it is not
known how many times the loop will
execute
 We developed two algorithms for searching
a list for the occurrence of a target value
 In the first algorithm, the list was sorted so we had
to stop the search if current value exceeded the
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Searching and Sorting a List
 In the while loop continuation condition, we
used logical AND
 continue the search if target not found AND
current entry is less than target AND the
current entry is not the last entry
 Incase of unsorted list, the condition
“current entry is less than target” is deleted
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Sorting a List
 “Insertion Sort” algorithm was
demonstrated in the class
 It was applied on a list of names.
 Insertion sort assumes the first name
belongs in the sorted section and remaining
names are in the unsorted section.
 It will take the members of the unsorted
section one by one and place them in the
sorted section at an appropriate location 10
*Binary and Hex Numbers
 Binary system has just two symbols 0 and 1
 It represents all values in patterns of 0 and 1
 Like decimal system, binary is also
positional number system
 It means that the position of a bit in a
pattern carries a weight
 Weights are powers of 2 increasing from
rightmost bit towards left, starting at 0 for
integer values(Example: 1101)
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*Binary and Hex Numbers
 Hex system has 16 symbols, all the way
from 0 to F
 It is also positional number system.
 For example, 1F, 1A, 2B
 Its digits carry weights expressed as powers
of 16 starting from 0 at the rightmost bit
position in the integer values
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*Converting Binary/Decimal
 Binary to decimal conversion assigns
position numbers. These are written as
powers of 2, then all products are added
 Example: 1001
 Conversion from decimal to binary involves
dividing the number repeatedly by 2 until a
value less than 2 is left. Writing the
remainders in each step from last value to
first value will give us the binary equivalent13
Digital Logic
 Boolean logic consists of three operations
AND,OR,NOT and two values 0 and 1
 AND operation results in a 1 only if BOTH
operands are 1
 OR operation results in a 1 if ANY operand
is equal to 1
 NOT operation turns a 1 into 0 and a 0 into 1
 Our focus is on converting real-life
situations into logical expressions
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Programming Language
Generations
 We talked about 2GL,3GL,4GL and 5GL
 These are different generations of
programming languages that evolved over
time
 2GL is the assembly language (mnemonics
such as MOV, ADD, STOR etc.)
 3GL are problem oriented and 4GL are user
oriented languages
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Software Engineering
 We introduced the motivation for software
engineering and why is it so important
 We looked at waterfall model and spiral
model of SE activities
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*WaterFall Model Diagram
Adapted from "Software Engineering
A Practitioner's Approach" by Roger
Pressman
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*The WaterFall Model
 This model is a sequence of stages
 During analysis, the user requirements are
identified and systems specs. are prepared
 During design, the number of modules and
their interconnection is finalized. The data
types and structure is specified
 During coding, actual programming is done
 Testing is done to make sure there are no
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errors (alpha-release and beta-release)
Spiral Model
 It was realized that the waterfall model is
not optimal as it is a one-way model
 If a problem is discovered in a later stage,
there is no way to go back and correct the
problem
 Therefore, spiral model was proposed in
which the SE activity occurs in a spiral thus
giving a chance to correct the mistakes
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Spiral Model Diagram
Adapted from "Software Engineering
A Practitioner's Approach" by Roger
Pressman
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Data Structures
 Arrays
 Contiguous lists
 Linked lists
 Stacks
 Binary Search Trees
 Expect one to two questions from these
topics, mostly specific
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Databases
 We covered network database model and
relational database model
 In the network model, several information
files are linked with physical disk addresses
 In relational database model, a search is
performed on a primary field in every file
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Encryption
 Symmetric key encryption was covered
with examples showing the use of XOR
logical operation of the value with a key for
both encryption and decryption
 DES was introduced that uses a 56-bit key
 The problem of key distribution led to
public-private key algorithms where
encryption and decryption is carried out
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with separate keys
Ethics
 Expect a short question related to ethics in
computing. Maybe a specific case
requesting your opinion
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How do you feel about
computers?
yep
THE
END
no
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