problem solving n analysis

8/3/2019 Problem Solving n Analysis

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Problem Solving Is the process of transforming the description of a problem

into the solution of that problem by using our knowledge ofthe problem domain and relying on our ability to select anduse appropriate problem-solving strategies, techniques, andtools."

Using computers

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Problem Solving Computers as a tool in problem solving:"

Extensive input"

Extensive output"

Method of solution is too complicated to

implement manually"

If done manually, it takes long time to solve"

Expect to use the same method of solution infuture to solve the same problem with different

inputs."

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Problem Solving Software Development method:

1. Requirement Specification"2. Analysis"3. Design"4. Implementation"5. Testing and verification"6. Documentation"

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1. Requirement Specification" Understanding what the problem is"

What is needed to solve it"

What the solution should provide"

If there is constraints and specialconditions"

How precisely we can define a problem depends on our degree

of familiarity with the problem domain"

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1. Requirement Specification"Example:"

A taxpayer can determineincome tax by using tax table if

the taxable income is less thanor equal to $50,000. However,if exceeds, use the tax rateschedules. Tax rate schedules

depend on filing status."

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1. Requirement Specification"Filing Status Over But Not Over Tax

Single 49,300 - 11,158 + 31% of amt over 49,300

Married filing jointly 34,000

82,150

82,150

-

5,100 + 28% of amt over 34,000

18,582 + 31% of amt over 82,150

Married filing separately 41,075 - 9,291 + 31% of amt over 41,075

Head of household 27,300

70,450

70,450

-

4,095 + 28% of amt over 27,300

16,177 + 31% of amt over 70,450

7

Taxable Income

Prompt user to enter taxable amount and read amount

Display menu filing status code

Read status code

Compute tax

Output results

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2. Analysis"☻ Identify:" Inputs to the problem"

Outputs expected from the solution"

Constraints"

Formulas"

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2. Analysis"Example"

Inputs – taxable income and filingstatus, interactive input."

Outputs – filing menu and final output :

taxable income, filing status, andcomputed income tax."

Constraints – should not accept less50,000, filing code should be 1,2,3,4."

Formulas – tax rate schedule."

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3. Design

Algorithm

"Is a sequence of a finite number of steps arranged in a specificlogical order, which, when executed, produce the solution for aproblem."

Unambiguousness"

Generality"

Correctness"

Finiteness"

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3. Design

Representing Algorithm"

11

pseudocodewords

descriptions

flowchart

graphical

descriptions

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3. Design


pseudocode "

Is a semiformal, English-like language with alimited vocabulary that can be used to design

and describe algorithms"

pseudocode language must:"

Limited vocabulary"

Simple and easy to learn"

Capable of describing complex problems"

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3. Design

Pseudocode language has 3 control structures:"

1)"

Sequence"

2) "Selection "

3) "Repetition"

13

Is a series of steps or statements that are executed

in the order in which they are written in an algorithm.

Define two courses of action, depending on the outcomeof a condition. A condition is an expression that, when

evaluated, computes to either true or false.

Specifies a block of one or more statements that are

repeatedly executed until a condition is satisfied.

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3. Design

Sequence Control Structure"

14

Is a series of steps or statements that are executed

in the order in which they are written in an algorithm.

beginread taxable income

read filing status

compute income tax

print income tax

end

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3. Design

Selection Control Structure"

15

if conditionthen-part

else

else-part

end_if

Define two courses of action, depending on the outcome

of a condition. A condition is an expression that, when

evaluated, computes to either true or false.

if conditionthen-part

end_if

if status is equal to 1

print “Single”end_if

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3. Design

Selection Control Structure"

16

if income less than or equal to 82,150

begin

compute tax = 5100 + 0.28 * (income – 34000)

print “ Tax rate is 28%”

end

else begin

compute tax = 18582 + 0.31 * (income – 82150)

print “ Tax rate is 31%”

end

end_if

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3. Design

Nested Selection Control Structure"

17

Is a basic selection structure that contains other if/else structure in its then-part or else-part


print “single”

else if status is equal to 2

print “married filing jointly”else if status is equal to 3

print “married filing separately”else if status is equal to 4

print “head of household”

else

print “error in status”

end_if


print “single”

end_if

if status is equal to 2 print “married filing jointly”

end_if


print “married filing separately”

end_if if status is equal to 4

print “head of household”if status is less than 1

print “error in status”

end_if

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3. Design

Repetition Control Structure"

18

while condition

loop-body

end_while

Specifies a block of one or more statements that are

repeatedly executed until a condition is satisfied.

Define loops using while

read income

while income is less than 50000

begin

print”please enter taxable income”

read incomeend

end_while

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Pseudocode

Conventions:" Includes keywords describing operations and operands;

compute, set, initialize, add, begin, end, while, end- while, if, end-if, then, else, print, read.!

Each statement in one line"

Enclose block statement"

Indent continuous statement"

Unambiguous and easy to understand"

19

if nombor is 10

begin

print “The number”

print “is Ten”

end

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3. Design


Flowchart" Is a graph consisting of geometrical shapes

that are connected by flow lines."

The shapes represent types of statements"

Details statements is written inside the shapes"

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Flowchart

Notations:

Syntax Semantic

21

begin/end

process

input/output

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Flowchart

Notation

Syntax Semantic

22

condition

continue

flow

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Pseudocode

begin

Statement_1

Statement_2

…

…

Statement_n

end

Flowchart

23

Flowchart Sequence structure

Statement_1 Statement_nStatement_2

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Pseudocode

if condition

then-part

else

else-part

end_if

Flowchart

24

Flowchart Selection structure

else-part then-part

condition truefalse

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Pseudocode

if condition

then-part

end_if

Flowchart

25

Flowchart Selection structure (missing else-part)

then-part

condition truefalse

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Pseudocode

while condition

loop-body

end_while

Flowchart

26

Flowchart Repetition structure (0 or more)

loop-bodycondition

true

false

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Pseudocode

begin

loop-body

while condition

end_while

Flowchart

27

Flowchart Repetition structure (at least once)

loop-body

condition

true

false

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Pseudocodestart

read 2 numbers

compute total

compute multiplication

compute average

print results

end

Flowchart

28

Examples:

Total = no1 + no2

Multi = no1 * no2

Ave = Total/2

begin

Read no1

Read no2

end

Print results

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Pseudocode

begin

read mark

compute grade

if grade >= 2.0

print pass

end

Flowchart

29

example

compute grade

grade >= 2.0

true

false

read mark

“pass”

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Pseudocode

begin

read mark

compute grade

if grade >= 2.0

print pass

end

Flowchart

30

example

compute grade

grade >= 2.0

true

false

read mark

“pass”

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31

True

print total, average

count < 5

Set count 0

Set total 0Set average 0

begin

total = total + mark

read mark

count = count + 1

false

average = total/count

end

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Repetition Two ways to control repetition

Sentinel value

Unique value

Unknown number of looping

counter

Control the number of looping

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Pseudocode - sentinel begin

read StuNum

while (StuNum not equal–999)

begin_while

read test_mark

read assign_mark

compute coursework

read the next StuNum

end_while

end

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Pseudocode - Counter begin

StuTot←

0 read StuNum

while (StuTot <= 60)

begin_while

read test_mark

read assign_mark

compute coursework

accumulate StuTot

read the next StuNum

end_while

end

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Top-Down StepwiseRefinement

Structure Chart

Use divide-and-conquer strategy to split the problem intosmaller subproblems

Refine the subproblems individually

Combine all refinements

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4. Implementation

Translating each step in algorithm into computerlanguage computer program"

Computer program"

is a sequence of finite number of statementsexpressed in a programming language in a specific

logical order that, when executed, produce thesolution for a problem."

Programming Errors"

Design errors"

Syntax Errors"

Run-time errors"

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5. Testing and verification

Testing"

Is the process of executing a program todemonstrate its correctness."

Use test data"

Verification" Is the process of ensuring that a program

meets user requirements."

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6. Documentation

Why?"

You are likely to return to this program in future"

In your absence, easier for others to refer to"

Others may need to maintain the program"

Easier to refer for corrections"

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6. Documentation

Consists of:"

Requirements specification"

Descriptions of I/o, constraints and formula"

Pseudocode"

Source program"

Sample test"

Userʼs guide"

39ms_2010

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