ALGORITHMS AND FLOW CHARTS

Adapted from the slides Prepared by Department of Preparatory year

Prepared by: lec. Ghader Kurdi

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Programming language

• Programming language is an artificial language that specifies instruction to be executed on a computer.

• There are two types of programming languages:• Low level languages• High level languages

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Low level language

• Low level language is a language that is machine-dependent and/or that offers few control instructions and data types.

• Each statement in a program written in a low-level language usually corresponds to one machine instruction.

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Computer Languages

• There are many types of computer languages, which can be categorized into the following four types:-

• Low-Level Languages (1st & 2nd Generation Languages)• High-Level Languages (3rd Generation Languages)• User-Friendly Languages (4th Generation Languages)• Object-Oriented Languages (5th Generation Languages)

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Main operation of high level language program

• Input operations:• Like input, read

• Output operations:• Like write, print

• Arithmetic operations:• Like add, subtract, multiply etc....

• control transferring operations:• Like “GO TO”, conditional, non-conditional etc....

• Looping:• Like repeat, do while, for, etc...

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Main step in developing program

• Problem understanding• Algorithm developing• Program writing• Program editing• Program compiling• Program running• Testing and debugging

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What an Algorithm is ???

“Sequence of precise instructions which leads to a solution is called an algorithm.”

or“An algorithm is a set of steps that defines how a task is to performed.”

Example:Steps (algorithm) for preparing a cake.Steps (algorithm) for calculating the area of a rectangle.Steps (algorithm) to solve a first degree equation.Steps (algorithm) to solve a second degree equation

using delta.

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What an Algorithm is??? • In other words, algorithm is a method of representing the

step-by-step logical procedure for solving a problem.

• An algorithm is a recipe for finding the right-answer to a problem or to a difficult problem by breaking down the problem into simple cases.

• An algorithm can be written in English like sentences or in any standard representation. Sometimes, algorithm written in English like languages is called Pseudo Code.

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What an Algorithm is??? • According to D.E. Knuth, a pioneer in the computer science

discipline, an algorithm must possess the following properties: (i) Finiteness: An algorithm must terminate in a finite number of steps(ii) Definiteness: Each step of the algorithm must be precisely and unambiguously stated(iii) Effectiveness: Each step must be effective, in the sense that it should be primitive (easily convertible into program statement) can be performed exactly in a finite amount of time.(iv) Generality: The algorithm must be complete in itself so that it can be used to solve all problems of a specific type for any input data.(v) Input/output: Each algorithm must take zero, one or more quantities as input data produce one or more output values.

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Algorithm Representation

• There are many ways in which we may represent an algorithm;

• We use many techniques to represent an algorithm in computer programming. The techniques that will study are: Flowchart Pseudocode

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Some verbs used in Pseudocode

• Get, Read used when a computer is required to receive information or input from a particular source• Put, Output, Display, Print used when the computer

is required to receive information or input from a particular source • Compute, Calculate used when when the computer

is required to perform arithmetic• Initialise, Set used to give data an initial value • If used to select one of two alternate actions• Dowhile, Enddo used to repeat a group of actions

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Pseudocode Example

What is algorithm for calculating the area of a rectangle ?

1. Get the values width, height

2. Calculate the value of area = width * height

3. Display the value of the area

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What is algorithm for solving a first degree equation (AX+B = 0) ?

1. Read the values A,B

2. Check if A=0 (if yes there is no equation) therefore no

equation to be solved (end processing).

3. Check if B=0 (if yes X=0 and end processing).

4. Calculate the value of X= -B/A

5. Print the value of : X

Pseudocode Example:

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Why Flowcharts:

The flowchart is graphical representation of the steps required for an algorithm or program.

The flowchart is characterized by:

Clarify the program logic

Identify alternative processing methods

Serve as guide for program coding

Serve as documentation

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Principals of Flowchart

1. Simplicity:- Easy to put on paper- Easy to draw- Readable and meaningful

2. Organization:- putting ideas together and organizing those ideas in logical way.

3. Planning:- flowchart helps for looking the program in deeper and global way.

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General Concepts

Flowchart must be characterized by the following:

1. The major element of the project.

2. Elements are clearly labeled.

3. Sequence of element must be clear.

4. No gap or dead ends.

5. Sequence of elements must be in logical form.

6. Flowchart must be used correctly.

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No Name Symbol Usage

1 Ellipse Start/Stop

2 Rectangle Expressions

3 Parallelogram

Input (Read) / Output(Print)

4 Rhombus Conditional checking

5 Arrow Flow of solution

6 Circle Connector

7 Elongated Hexagon Continue

8 Rectangle with bars

Procedure / Function call

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Levels of Program Flowchart

1. Simple sequential flowchart.

2. Branched flowchart.

3. Simple-loop flowchart.

4. Multi-loop flowchart.

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Simple sequential flowchart

• It is simplest level which contain the sequence of steps without loops or branch.

• The flowchart comes in straight line from the beginning to the end.

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Example1: Algorithm for reading student name

1. Start

2. Read student name

3. End

start

Read student name

Stop

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Example2: Algorithm for calculate the area of circle

1. Start

2. Read value of R

3. Set PI equal to 3.14

4. Calculate Area=PI*R*R

5. Print R, Area

6. Stop

start

Read R

Stop

PI=3.14

Area=Pi*R*R

Print R, Area

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Example3: Write an algorithm and draw the flow chart to add two numbers.

Algorithm:

1.Start

2.Read a, b

3.Calculate c=a + b

4.Print c

5.Stop

Flow chart:

Start

c = a+ b

Print c

Read a, b

Stop

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Example4: Write an algorithm and draw the flow chart to find the circumference of circle

Algorithm:

1.Start

2.Read r

3.Calculate c= 2*3.14 * r

4.Print c

5.Stop

Start

c =2 * 3.14 * r

Print c

Read r

Stop

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Branched flowchart

• It is branched flowchart, when there is a condition statement in the program.

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Example5: Draw flow chart for evaluating the following functions: F(X)=x if X>=0, F(X)= -X if X<0

1. Start

2. Read X

3. If X>=0 then go to step 4, else step 5

4. Calculate F(X)=X than go to step 6

5. Calculate F(X)= -X

6. Print X, F(X)

7. Stop

start

Read X

Stop

F(x)= -x

Print x, F(x)

X>=0

F(x)=x

A

Yes

No

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Example6: Write an algorithm and draw the flowchart that reads three numbers and print the value of the largest number.

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Simple-loop flowchart

• It is a flowchart which contain iteration or repetitions.

• It is usually called loop flowcharts.

• In this type we need to repeat some operation several times using the same set of operation.

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Example7: write an algorithm and draw a flowchart for printing 10 integers starting from 1

Algorithm:

1.Start

2.Take the initial value of A=1

3.Check if A>=10 if yes and

If no print the number and increment A by 1

start

EndPrint A

A>=10?

A=A+1

A=1

Yes

No

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Multi-loop flowchart

• Looping is used to manage a loop to fulfill a repetition under a definite condition

Algorithm Sample1.Counter i 2. Any Initial value → ( Set i =0) 3.Final Value (N) → (Set N= 10) 4.Increment or Decrement Value (M) → (Set M=1)

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Exercises

Write algorithms and draw flowcharts to represent the logic of the following programs:

• Calculate and print the sum of numbers from 1 to 100 .

• Accepts a number and display “Even Number” if the number entered is even. Otherwise the program will display “Odd Number”.

• Asks the user to input the password “hello”. Only if the password is correct, will display “Welcome”.

• Compares two numbers to see if one is greater than the other and print the result of the comparison.