Best Techniques To Design Programs - Program Designing Techniques
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Transcript of Best Techniques To Design Programs - Program Designing Techniques
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Program Designing techniquesAuthor : Aamir Saleem Ansari
Web : www.techora.net
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Program Designing techniques
Pseudocode AlgorithmFlowchart
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Designing techniques
A typical programming task can be divided into two phases:
Problem solving phase produce an ordered sequence of steps that
describe solution of problem this sequence of steps is called an algorithm
Implementation phase implement the program in some programming
language
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Steps in Problem Solving
First produce a general algorithm (one can use pseudocode)
Refine the algorithm successively to get step by step detailed algorithm that is very close to a computer language.
Pseudocode is an artificial and informal language that helps programmers develop algorithms.
Pseudocode is very similar to everyday English.
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Pseudocode & Algorithm
Example 1: Write a pseudocode and an algorithm to convert the length in feet to inches.
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Example 2
Pseudocode: Input the length in feetCalculate the length in inches by
multiplying length in feet with 12Print length in inches.
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Example 2
Algorithm Step 1: Input L_ftStep 2: L_inches L_ft x 12Step 3: Print L_inches
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The FlowchartA schematic representation of a sequence of
operations, as in a manufacturing process or computer program.
It is a graphic representation of how a process works, showing, at a minimum, the sequence of steps.
A flowchart consists of a sequence of instructions linked together by arrows to show the order in which the instructions must be carried out.
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Cont…
Each instruction is put into a box. The boxes are different shapes depending upon what the instruction is.
Different symbols are used to draw each type of flowchart.
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Cont…
A Flowchartshows logic of an algorithmemphasizes individual steps and their
interconnectionse.g. control flow from one action to the next
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Flowchart Symbols
Basic
Oval
Parallelogram
Rectangle
Diamond
Hybrid
Name Symbol Use in Flowchart
Denotes the beginning or end of the program
Denotes an input operation
Denotes an output operation
Denotes a decision (or branch) to be made. The program should continue along one of two routes. (e.g. IF/THEN/ELSE)
Denotes a process to be carried oute.g. addition, subtraction, division etc.
Flow line Denotes the direction of logic flow in the program
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Example 2
Write an algorithm and draw a flowchart to convert the length in feet to centimeter.
Pseudocode: Input the length in feet (Lft)Calculate the length in cm (Lcm) by
multiplying LFT with 30Print length in cm (LCM)
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Example 2
Algorithm Step 1: Input L_ftStep 2: Lcm L_ft x 30 Step 3: Print L_cm
START
InputL_ft
Lcm L_ft x 30
PrintL_cm
STOP
Flowchart
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Example 3
Write an algorithm and draw a flowchart that will read the two sides of a rectangle and calculate its area.
Pseudocode Input the width (W) and Length (L) of a
rectangle Calculate the area (A) by multiplying L with W Print A
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Example 3
Algorithm Step 1: Input W,LStep 2: A L x W Step 3: Print A
START
InputW, L
A L x W
PrintA
STOP
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Example 4
Write an algorithm and draw a flowchart that will calculate the roots of a quadratic equation
Hint: d = sqrt ( ), and the roots are: x1 = (–b + d)/2a and x2 = (–b – d)/2a
2 0ax bx c
2 4b ac
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Example 4
Pseudocode: Input the coefficients (a, b, c) of the
quadratic equationCalculate dCalculate x1Calculate x2Print x1 and x2
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Example 4
Algorithm: Step 1: Input a, b, c Step 2: d sqrt ( ) Step 3: x1 (–b + d) / (2 x a) Step 4: x2 (–b – d) / (2 x a) Step 5: Print x1, x2
START
Inputa, b, c
d sqrt(b x b – 4 x a x c)
Printx1 ,x2
STOP
x1 (–b + d) / (2 x a)
X2 (–b – d) / (2 x a)
4b b a c
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Decision Structures
The expression A>B is a logical expression it describes a condition we want to test if A>B is true (if A is greater than B) we take
the action on left print the value of A if A>B is false (if A is not greater than B) we
take the action on right print the value of B
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Decision Structures
isA>B
Print B
Print A
Y N
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IF–THEN–ELSE STRUCTURE
The structure is as followsIf condition then
true alternative else
false alternativeendif
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IF–THEN–ELSE STRUCTURE
If A>B then print A
else print B
endif
isA>B
Print B
Print A
Y N
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Relational Operators
Relational OperatorsOperator Description
> Greater than
< Less than
= Equal to
Greater than or equal to Less than or equal to
Not equal to
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Example 5
Write an algorithm that reads two values, determines the largest value and prints the largest value with an identifying message.
ALGORITHMStep 1: Input VALUE1, VALUE2Step 2: if (VALUE1 > VALUE2) then
MAX VALUE1else
MAX VALUE2endif
Step 3: Print “The largest value is”, MAX
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Example 5
MAX VALUE1
Print“The largest value is”,
MAX
STOP
Y N
START
InputVALUE1,VALUE2
MAX VALUE2
isVALUE1>VALUE2
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NESTED IFS
One of the alternatives within an IF–THEN–ELSE statementmay involve further IF–THEN–ELSE
statement
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Example 6
Write an algorithm that reads three numbers and prints the value of the largest number.
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Example 6
Step 1: Input N1, N2, N3Step 2: if (N1>N2) then
if (N1>N3) then MAX N1 [N1>N2, N1>N3]
else MAX N3 [N3>N1>N2]
endifelse
if (N2>N3) then MAX N2 [N2>N1, N2>N3]
else MAX N3 [N3>N2>N1]
endifendif
Step 3: Print “The largest number is”, MAX
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Example 6
Flowchart: Draw the flowchart of the above Algorithm.
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Flowchart
NO
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Example 7
Write and algorithm and draw a flowchart to read an employee name (NAME), overtime hours worked (OVERTIME), hours absent (ABSENT) and determine the bonus payment (PAYMENT).
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Example 7
Bonus ScheduleOVERTIME –
(2/3)*ABSENTBonus Paid
>40 hours>30 but 40 hours>20 but 30 hours>10 but 20 hours 10 hours
$50$40$30$20$10
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Step 1: Input NAME,OVERTIME,ABSENTStep 2: if (OVERTIME–(2/3)*ABSENT > 40 ) then PAYMENT 50 else if (OVERTIME–(2/3)*ABSENT > 30 && OVERTIME–(2/3)*ABSENT<= 40 ) then
PAYMENT 40 else if (OVERTIME–(2/3)*ABSENT > 20 &&
OVERTIME–(2/3)*ABSENT<= 30 ) then PAYMENT 30
Algorithm
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else if (OVERTIME–(2/3)*ABSENT > 10 &&OVERTIME–(2/3)*ABSENT<= 20) then
PAYMENT 20 else PAYMENT 10 endif
Step 3: Print “Bonus for”, NAME “is $”, PAYMENT
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Example 7
Flowchart: Draw the flowchart of the above algorithm?
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LOOPS
Computers are particularly well suited to applications in which operations are repeated many times.
If the same task is repeated over and over again a loop can be used to reduce program size and complexity
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Flowchart for finding the sum of first five natural numbers
( i.e. 1,2,3,4,5):
Example 8:
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Example 9
Flowchart to find the sum of first 50 natural numbers.
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Example 10
Write down an algorithm and draw a flowchart to find and print the largest of N (N can be any number) numbers. (Assume N to be 5 and the following set to be the numbers {1 4 2 6 8 })
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Algorithm:
Step 1: Input N Step 2: Input Current Step 3: Max Current Step 4: Counter 1 Step 5: While (Counter < N)
Repeat steps 5 through 8 Step 6: Counter Counter + 1 Step 7: Input Next Step 8: If (Next > Max) then
Max Next endif
Step 9: Print Max
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START
InputN, Current
Max Current
PrintMax
STOP
Y
Counter < NN
Counter 1
Counter Counter +1
InputNext
Next >Max
Y
N
Max Next
Flowchart
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Introduction to Computing