Lecture 4

Flow Charts

Flow Charts •A diagrammatic representation that illustrates the sequence of operations to be performed to get the solution of a problem.• Generally drawn in the early stages of formulating computer solutions. • Facilitate communication between programmers and business people. • Play a vital role in the programming of a problem and are quite helpful in understanding the logic of complicated and lengthy problems. • Once the flowchart is drawn, it becomes easy to write the program in any high level language. • Must for the better documentation of a complex program.

Flow Charts

A flow chart can be used to:

• Define and analyse processes.

• Build a step-by-step picture of the process for analysis, discussion, or communication.

• Define, standardise or find areas for improvement in a process.

Flow Charts

Symbols for drawing a flowchart:

Start or End of the program

Flow Charts


Computational Steps or Processing Function of a program

Flow Charts


Input or output operation

Flow Charts


Decision Making and Branching

Flow Charts


Connector or joining of two parts of program

Flow Charts


Magnetic Tape

Flow Charts


Magnetic Disk

Flow Charts


Off-page connector

Flow Charts


Flow lines

Flow Charts


Annotation (foot note)

Flow Charts


Display

Flow Charts

Guidelines in flowcharting - • In drawing a proper flowchart, all necessary

requirements should be listed out in logical order. • The flowchart should be clear, neat and easy to

follow. There should not be any room for ambiguity in understanding the flowchart.

• The usual direction of the flow of a procedure or system is from left to right or top to bottom.

Flow Charts

…Guidelines in flowcharting -

• Only one flow line should come out from a process symbol.

OR

Flow Charts

…Guidelines in flowcharting -

• Only one flow line should enter a decision symbol, but two or three flow lines, one for each possible answer, should leave the decision symbol.

Flow Charts

…Guidelines in flowcharting –

Only one flow line is used in conjunction with terminal symbol.

Flow Charts


Write within standard symbols briefly. As necessary, you can use the annotation symbol to describe data or computational steps more clearly.

This is confidential data

Flow Charts


• In case of complex flowchart, it is better to use connector symbols to reduce the number of flow lines. Avoid the intersection of flow lines.

• Ensure that the flowchart has a logical start and finish.

• It is useful to test the validity of the flowchart by passing through it with a simple test data.

Flow Charts

Advantages Of Using Flowcharts :

• Effective communication• Effective analysis• Proper documentation• Efficient Coding• Proper Debugging• Efficient Program Maintenance

Flow Charts

Limitations of using Flowcharts :

1.Complex logic: Sometimes, the program logic is quite complicated.

2.Alterations and Modifications: Alterations may require re-drawing completely.

3.Reproduction: As the flowchart symbols cannot be typed, reproduction of flowchart becomes a problem.

Flow Charts

Example 1.

Draw a flowchart to find the sum of first 50 natural numbers.

Example 2

Draw a flowchart to find the largest of three numbers A,B and C.

Flow Charts

Example 3Draw a flowchart for computing factorial of a given number

Flow Charts

AssignmentFill in the blanks- 1. A program flowchart indicates the_________ to be performed

and the __________ in which they occur. 2. A program flowchart is generally read from _____________ to

________________ 3. Flowcharting symbols are connected together by means of

___________________ 4. A decision symbol may be used in determining the

____________ or ___________ of two data items. 5. __________ are used to join remote portions of a flowchart 6. ____________ connectors are used when a flowchart ends on

one page and begins again on other page 7. A ________ symbol is used at the beginning and end of a

flowchart. 8. The flowchart is one of the best ways of ________ a program.. 9. To construct a flowchart, one must adhere to prescribed

symbols provided by the __________ . 10.The program uses a ____________ to aid it in drawing

flowchart symbols.

Answers

• Operations, sequence • Top, down • Flow line • Equality, inequality • connectors • Off -page • Terminal • documenting • ANSI (American National Standards Institute) • Flowcharting template

Structured English

Structured English• Structured English is a tool used to

represent process logic. • Syntax rules are not very strict & an English

statement is used to specify an action. • The main aim is to allow easy readability,

which helps in documentation.

Two building blocks of Structured English:1. Structured logic or instructions organized

into nested or grouped procedures 2. Simple English statements such as add,

multiply, move

Structured EnglishFour conventions to follow when using Structured

English:

• Express all logic in terms of sequential structures, decision structures, or iterations.

• Use upper case for keywords such as: IF, THEN, ELSE, DO, DO WHILE, DO UNTIL, PERFORM

• Indent blocks of statements to show their hierarchy (nesting) clearly.

• When words or phrases have been defined, underline those words or phrases to indicate that they have a specialised, reserved meaning.

The Flow of Structured English

User

Structured English

Analyst

Programs

Programmer

Plain Englis

h

Pseudocode

…Structured English

The conventions are used in writing structured English:

1. Imperative Sentences: Store the data in database.

2. Arithmetic & Relational Operations : Common symbols of mathematics are used in structured English such as- + for add, - for subtraction etc. and =, >=, != etc. are used for relational operations.


3. Decision Structures: If Then Else, Select Case

4. Repetion: Loops

There are various forms in which structured english can be implemented to solve the problem. e.g. Algorithm, Flowchart, pseudocode.


Writing Structured EnglishRepetition

DO

statements …

UNTIL end-condition

or

DO WHILE

statements …

END DO

Conditions

IF … THEN …

statements …

ELSE

statements …

END IF

or

SELECT CASE 1 (conditions)

statements …

CASE 2 …

statements …

END SELECT

Pseudocode

Pseudocode

• An outline of a program, written in a form that can easily be converted into real programming statements.

• Pseudocode cannot be compiled nor executed, and there are no real formatting or syntax rules.

…Pseudocode

• It enables the programmer to concentrate on the algorithms without worrying about all the syntactic details of a particular programming language.

• Flowcharts can be thought of as a graphical form of pseudocode.

Example of Pseudocode

Regular code (written in PHP):<?php if (is_valid($cc_number)) { execute_transaction($cc_number, $order); } else { show_failure(); } ?> Pseudocode:if credit card number is valid

execute transaction based on number and order else show a generic failure message end if

Technology

Lecture 4