algorithm-and-flowcharting.pdf

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Algorithm and Flowcharting
BS Civil Engineering (Polytechnic University of the Philippines)
Studocu is not sponsored or endorsed by any college or university
BS Civil Engineering (Polytechnic University of the Philippines)
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Lecture in
COMPFUND
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Phases of SDLC
System Development Life Cycle
◼Preliminary Investigation
◼Analysis
◼Design
◼Development
◼Implementation
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Activities Involve in
Programming
◼ Understand the problem.
◼ Plan the logic.
◼ Code the program.
◼ Compile the program into machine
language.
◼ Test the program.
◼ Put the program into production.
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Activities involve in
Programming
Understanding the Problem
◼ Before writing the program the programmer must first
understand the problem.
◼ Satisfy the user’s need
◼ One of the most difficult task since description of what
is needed may be vague, or worse yet, the user may
not even know what he/she wants.
◼ A good programmer is part counselor, and part
detective.
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Programming
Plan the Logic
The process of planning for the solution of the
problem.
◼They are referred to as “ALGORITHMS”
◼Two most common tools are FLOWCHARTS and
PSEUDOCODE.
◼ Involves writing down steps (in English).
◼ The programmer doesn’t worry about syntax at this
point, just the sequence of events that will lead from
available input to the desired output.
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Programming
Code the Program
◼ There are over 400 programming languages that
exist.
◼Most programming languages have translators
also known as compiler and interpreters.
◼Pascal, C, C++, Visual Basic, Cobol, etc.
◼ The part in which the programmer worry about the
correct syntax; command, punctuation, spelling, etc.
◼ The actual construction of the source code.
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Programming
Compile the program into Machine Language
◼ Machine language - the only language a machine
knows.
◼Its consists of 0’s and 1’s.
◼ Compiler is a special program that translates high-level
language instructions into machine language.
◼ Compiler catches all syntax errors.
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Programming
Test the Program
◼ Check for logical errors.
◼ The use of sample data to see whether the
programming is running properly.
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Programming
Put the Program into Production
◼ The organization can now use the program.
◼ Training personnel to use the program.
◼ Running the program using the actual data.
◼ Test for user’s approval.
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Algorithm
◼ A sequence of well-understood steps that one takes to
do something.
◼ A set of instructions for a person to follow in order to
accomplish a certain task.
◼ A sequence of instructions that tell how to solve a
particular problem.
◼ It is a finite set of instructions that specify a sequence of
operations to be carried out in order to solve a specific
problem or class of problems.
◼ Examples:
◼ directions for going to a certain place
◼ baking a chocolate cake
◼ computing income tax
◼ searching for a name in a telephone directory
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Example:
Prepare a Cup of Coffee
◼ Step 1: Fill kettle with water.
◼ Step 2: Turn on stove.
◼ Step 3: Put kettle on stove.
◼ Step 4: If water is boiling proceed to step#5 otherwise wait.
◼ Step 5: Turn off stove
◼ Step 6: Fill mug with boiled water
◼ Step 7: Put 1 tsp. of coffee in mug.
◼ Step 8: With sugar, put 2 tsp. of sugar in mug, otherwise proceed
to step#9.
◼ Step 9: With milk, pour 1 tbsp. of milk in mug, otherwise proceed to
step#10.
◼ Step 10: Stir contents of mug
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Characteristics of an Algorithm
◼ Specify each step or instruction exactly.
◼There must be no ambiguity.
◼The instructions must be clear.
◼ There must be a finite number of steps.
◼The algorithm must terminate.
◼There must be a stopping point.
◼ There must be an output.
◼The algorithm must produce the correct result.
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Flowcharting
What is Flowcharting?
◼ A graphical representation of the logical steps that solves a
problem.
◼ Programmers use flowcharts to understand the logic
processing of data.
◼ To visualize how statements in a program are interrelated.
◼ Although time consuming, it’s the best tool for beginners.
◼ Use of symbol and phrases to designate the logic of how a
problem solved.
◼ A common method for defining the logical steps of flow within a
program by using a series of symbols to identify the basic
input, process and output (IPO’s) function within a program.
◼ A diagram representing the logical sequence in which a
combination of steps or operation is to be performed. It is a
blueprint of the program.
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Flowcharting
Types of Flowcharts
◼ Program Flowcharts
◼Depicts the detailed logical flow of process in a program.
◼ System Flowcharts
◼Shows the logic flow of data from one source to another.
◼Divided into functions of departments or personnel.
◼Symbols are used to represent documents used and
operations undertaken.
◼Highlights excessive information flow, duplication of
information stored in different locations and reasons for
delay of transactions.
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Basic Flowcharting Symbols
Terminal block
Input/Output block
Process symbol
Decision symbol
On-page Connector
Off-page Connector
Initialization symbol
Flow lines
Flowcharting
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◼ Terminal
- used to signify the beginning
and end of flowchart
Flowcharting
OVAL
START
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◼ Preparation/Initialization
- signifies the preparation of data
- Used to select initial conditions
- Used to represent instructions or
group of instructions that will
alter or modify a programs
course of execution
Flowcharting
Hexagon
SUM=0
PRODUCT=0
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◼ Input/Output
-shows input and output.
Data are to be read into the
computer memory from an
input device or data are to
be passed from the memory
to an output device.
Flowcharting
Parallelogram
Read A
Print A
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◼ Process/Processing
-performs any calculations hat
are to be done.
Flowcharting
Rectangle
Sum = A+B
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◼ Decision
-signifies any decisions that are to
be done. Two alternative
execution paths are possible.
The path to be followed is
selected during the execution by
testing whether or not the
condition specified within the
outline is fulfilled.
Flowcharting
Diamond
If x>5
T F
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◼ On-page Connector
-show the entry or exit point of the
flowchart. A non-processing
symbol used to connect one part
of a flowchart to another without
drawing flowlines. Conserves
space by keeping related blocks
near one another, reduces the
number of flowlines in complex
program and eliminates cross
lines from taking place.
Flowcharting
A
Small Circle
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◼ Off-page Connector
-designates entry or to exit
from one page when a
flowchart requires more
than one page.
Flowcharting
Pentagon
B
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◼ Flowlines
-signifies the process that is
to be executed next
Flowcharting
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Basic Flowcharting
◼ Almost every program involves the steps of input,
processing and output.
◼Example:
Get number
Answer = number *2
Print Answer
◼ Most flowcharts need some way to separate each step.
◼ Drawing different boxes around each statement is the
standard convention.
◼ Input operation are represented in a parallelogram. A
statement in English is written inside the parallelogram.
Flowcharting
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What are Variables?
◼ Memory allocations, the content of which may vary/change.
◼ The capability of memory variables to change its content
makes the computers and programming worthwhile.
◼ Because one memory location can be used over and over
again with different values, program instructions can be
written once and then used for thousands of problems.
◼ Giving names (for identification) may vary from one
programming language to another; some may allow
hyphens; others allows underscores; some languages allow
dollar signs, others don’t. There are languages that limits the
length of names to a variable.
Flowcharting
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Rules in naming variables...
◼ Must be one word.
◼ May contain letters, numbers, hyphens,
underscores.
◼ Must not start with a number.
◼ Must not contain a space.
◼ Must have some meaning.
Invalid Variable names
 interest rate - should be one word
 rate! - contains ! an invalid character
 xyxxx - although this is allowed, it doesn’t mean
or imply anything that it may hold.
 #total - should not start with a special character.
Flowcharting
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Types of Variables
◼ Numeric Variables
◼ The type of variable that can hold a number.
◼ In this example: Answer = number * 2
◼ Some languages allow additional types of data; Pascal and C
distinguish between integer or whole number numeric variables and
floating point, decimal and fractional numeric variables.
◼ Character, Text or String Variables
◼ Variables that can hold letters of the alphabet and other special
character such as punctuation marks.
◼ Example:
NAME = “WASHINGTON”
◼ Logical or Boolean Variables
◼ A special type of variable that can only have two values - TRUE or
FALSE.
Flowcharting
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Arithmetic Operators and Mathematical Statements
◼ Addition (+)
◼ Subtraction (-)
◼ Multiplication (*)
◼ Division (/)
◼ Modulus (%)
◼ A mathematical statement is composed of a left variable, an
assignment operator (usually in the form of an equal sign) a
series of operands(may be a set of the same variables or a new
set of variables, and /or constants) and (arithmetic) operators.
◼ Example:
x = x + 1
sum = a + b
Flowcharting
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Constants
◼ A constant is a value that never changes during the
execution of the program.
◼ Constants can be any type-numeric, alphabetic or
special symbols.
◼ Like variable, constants can be named. The computer
sets up a specific memory location to hold the value of
the constant.
◼ During the execution of the program, the constant is
referred to by name. Once the constant is given a
value, it cannot be changed during the execution of
the program.
Flowcharting
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Relational Operator
◼ A relational operator compares two values and
determines the relationship between them.
Operator Use Returns true if
> op1 > op2 op1 is greater than op2
>= op1 >= op2 op1 is greater than or equal to op2
< op1 < op2 op1 is less than op2
<= op1 <= op2 op1 is less than or equal to op2
== op1 == op2 op1 and op2 are equal
!= / not= op1 != op2 op1 and op2 are not equal
op1 not= op2
Flowcharting
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Logical Operators
◼ Use logical operators (also called Boolean operators) to
express relationships between search expressions.
Operator Use Returns true if
and cond1 and cond2 both condition should be true
or cond1 or cond2 either one of the condition is true
not (negation) not cond
! cond
Flowcharting
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ADVANTAGES OF USING
FLOWCHARTS
1. Communication: Flowcharts are better way of communicating the logic
of a system to all concerned.
2. Effective analysis: With the help of flowchart, problem can be analyzed
in more effective way.
3. Proper documentation: Program flowcharts serve as a good program
documentation, which is needed for various purposes.
4. Efficient Coding: The flowcharts act as a guide or blueprint during the
systems analysis and program development phase.
5. Proper Debugging: The flowchart helps in debugging process.
6. Efficient Program Maintenance: The maintenance of operating program
becomes easy with the help of flowchart. It helps the programmer to put
efforts more efficiently on that part
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LIMITATIONS OF USING
FLOWCHARTS
1. Complex logic: Sometimes, the program logic is quite
complicated. In that case, flowchart becomes complex and
clumsy.
2. Alterations and Modifications: If alterations are required
the flowchart may require re-drawing completely.
3. Reproduction: As the flowchart symbols cannot be typed,
reproduction of flowchart becomes a problem.
4. The essentials of what is done can easily be lost in the
technical details of how it is done.
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Draw a flowchart that will accept and display a number. Write
its equivalent algorithms.
Algorithm:
Step 1: Read in the value of N.
Step 2: Print the value of N.
START
READ N
PRINT N
END
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Draw a flowchart that will compute and display the sum and
product of two numbers. Write its equivalent algorithm.
Algorithm:
Step 1: Initialize Sum and Product
into 0.
Step 2: Read in the values of A and
B.
Step 3: Compute the sum by
adding A and B then compute the
product by multiplying A and B.
Step 4: Print the computed value of
Sum and Product.
START
Read A,B
Print Sum,
Product
END
Sum = 0
Product = 0
Sum = A + B
Product = A * B
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Construct a flowchart that will convert an inputted number in
Fahrenheit to its equivalent measure in Celsius.
Formula: C = (5/9)*(F-32)
Algorithm:
Step 1: Initialize Celsius into 0.
Step 2: Read in the value of
Fahrenheit.
Step 3: Compute the value of
Celsius.
Step 4: Print the computed value of
Celsius.
START
Read Fah
Print
Celsius
END
Celsius=0
Celsius=(5/9)*
(Fah-32)
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Draw a flowchart that will input values for A and B. Compare two
values inputted and print which of the values is higher including the
remark “Higher”. Write its equivalent algorithm.
Algorithm:
Step 1: Read the values of A and B.
Step 2: Test if A is greater than B.
Step 3: If A is greater than B, A is higher.
However, if A is less than B, B is higher.
Step 4: Print the number and the remark
“Higher”
START
Input A,B
Print A,
“Higher”
END
A > B
Print B,
“Higher”
T
F
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Draw a flowchart that will input grade of student and determine
whether the grade is passed or failed. Print the name, grade and
remarks of student. Write its equivalent algorithm.
Algorithm:
Step 1: Initialize name and remarks into blanks.
Step 2: Read in values for Grade and Name.
Step 3: Test if Grade is greater than or equal to 60.
Step 4: If Grade is greater than or equal to 60,
remark is “Passed”. However, if Grade is below
60, remark is “Failed”.
Step 5: Print the name, grade and remarks.
START
Read Name,
Grade
END
If Grade
>60
Print Name,
Grade, Remarks
Name=“ “
Remarks = “ “
Remarks =
“Failed”
Remarks =
“Passed”
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SEATWORK
◼ DEI Manufacturing Company plans to give a year-
end bonus to each of its employee. Draw a
flowchart which will compute the bonus of an
employee. Consider the following conditions: If
the employee’s monthly salary is less than 2,000
pesos, the bonus is 50% of the salary; for
employees with salaries greater than 2,000 pesos,
the bonus is 1,500 pesos. Print the name and the
corresponding bonus for each employee. Write
each equivalent algorithms.
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Pseudocode
◼ uses everyday language to prepare a brief set of instructions
in the order in which they will appear in the finished program.
◼ It is an abbreviated version of actual computer code (that's
why it is called pseudocode).
◼ Pseudocode looks more like a real program than the flowchart
does. It allows the programmer to focus on the steps required
to solve a program rather than on how to use the computer
language.
◼ An advantage of pseudocode is that it can be used to
describe a program to a nontechnical user and can still
provide guidelines for the writing of program code.
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Pseudocode
◼ A textual presentation of a flowchart
◼ Close to a natural language
◼ The control structures impose the logic
◼ May become a part of the program documentation
◼ Could be translated into a program
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