Programming and Design Principles
Software Development programme

Muhammad ibn Musa
Al'Khowarizmi, a
Tashkent cleric who in
the twelfth century
developed the concept of
a written process to be
followed to achieve some
goal, and published a
book on the subject that
gave it is modern name - algorithm.
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An algorithm is merely the sequence of
steps taken to solve a problem
◦ Two parts
 Actions to be executed
 Order in which those actions are to be done
◦ Computational steps that transform the input
data into useful output data.
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Algorithms are not programs
◦ They need to be coded in a programming
language like C++
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Programmers arrive at these solutions by
using one or more of these devices:
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Logic flowcharts
Structure charts
Pseudocode (sue-dough'-code)
Structured Programming
Solutions to problems need to be developed
before code is written
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C++ syntax can obscure understanding
◦ Write out solutions intuitively – on paper
◦ Use flowcharts or pseudocode
◦ Translate ideas to C++ syntax on paper
Try to NEVER compose code at the terminal
Don't try to crate the perfect solution on the
first try – it's too difficult
◦ Begin with a partial solution that runs
◦ Make it better iteratively through refinement
 Prototyping

Spend a little more on an organized software
development approach to save a lot during
testing, maintenance, and support phases

Pseudocode –
◦ Make a detailed description of your
algorithm’s logic before worrying about C++
syntax and data layout.
◦ An algorithm you develop using pseudocode
should be capable of implementation in any
procedural programming language
 Pseudocode is generally independent of the
implementation language
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Flowcharts –
◦ A graphical layout of the algorithm is often
very useful in spotting “illogical” logic!
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Forms of documentation used to build and
communicate the detailed parts your
structured designs
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A graphical representation of an algorithm.
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Drawing a flowchart gives the programmer
a good visual reference of what the
program will do
Flowcharts serve as program documentation
Flowcharts allow a programmer to test
alternative solution to a problem before
coding
Flowcharts provide a method for easy desk
checking

These represent the
flow of logic in a
program and help
programmers “see”
program design.
Common Flowchart Symbols
Terminator. Shows the starting and ending points of the program. A terminator has
flow lines in only one direction, either in (a stop node) or out (a start node).
Data Input or Output. Allows the user to input data and results to be displayed.
Processing. Indicates an operation performed by the computer, such as a variable
assignment or mathematical operation. With a heading – an internal subroutine
Decision. The diamond indicates a decision structure. A diamond always has two
flow lines out. One flow lineout is labeled the “yes” branch and the other is labeled the
“no” branch.
Predefined Process. One statement denotes a group of previously defined statements.
Such as a function or a subroutine created externally
Connector. Connectors avoid crossing flow lines, making the flowchart easier to read.
Connectors indicate where flow lines are connected. Connectors come in pairs, one with
a flow line in and the other with a flow line out.
Off-page connector. Even fairly small programs can have flowcharts that extend several
pages. The off-page connector indicates the continuation of the flowchart on another
page. Just like connectors, off-page connectors come in pairs.
Flow line. Flow lines connect the flowchart symbols and show the sequence of operations
during the program execution.
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Top to bottom and left to right
◦ Draw the flowchart the way you like to read
◦ Use arrowheads on flow lines whenever the flow is
not top to bottom, left to right
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Be neat ! Use graphics software
Avoid intersecting lines
Start
or
Preparation Symbol
sum=
Input price
sum=sum+price
Yes
Terminal Symbol
More
items?
No
tax=sum x 0.0725
total=sum+tax
Output sum, tax,
and total
Stop
I/O Symbol
Process Symbol
Decision Symbol
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Time consuming
A program flowchart shows how the input
becomes output, but it does not show why a
particular step is done
Flowcharts are subjective
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Pseudocode is an artificial and informal
language that helps programmers develop
algorithms.
◦ Pseudocode is a "text-based" detail (algorithmic)
design tool.
◦ An English description of an algorithm in sufficient
detail to allow its implementation to be easily
written.
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This device is not visual but is considered a
“first draft” of the actual program.
Pseudocode is written in the programmer’s
native language and concentrates on the logic
in a program—not the syntax of a
programming language.
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There is no standard pseudocode
The rules of Pseudocode are generally
straightforward
◦ Should be easily read and understood by nonprogrammers
◦ All statements showing "dependency" are to be
indented.
 These include while, do, for, if, switch
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You need to reach a balance between
excessive and insufficient detail.
◦ In some cases you only need a skeleton of the logic
and in other cases you may want to show the
intricacies of your algorithm
◦ Write what is necessary to understand and
communicate the essential parts of your algorithm
without becoming bogged down in detail
◦ Statements are written in a simple English-like
language
◦ Each instruction is started on a separate line
◦ Logic-showing keywords are written in UPPER
CASE or typed in BOLD UPPERCASE
 (e.g. IF, THEN, FOR, DO etc.)
 These are the only uppercase words in this form of
pseudocode.
◦ Indentation is used to show structure
◦ Instructions are written from top to bottom,
with only one entry point and one exit point
◦ Logically related groups of instructions can be
formed into modules and given a name
sum=0
While More items do
Input price
sum=sum+price
End While
tax=sum x 0.0725
total=sum+tax
Output sum, tax, total
1.
2.
3.
4.
5.
6.
7.
8.
Make the pseudocode languageindependent
Indent lines for readability
Make key words stick out by showing
them capitalized, in a different color or
a different font
Punctuation is optional
End every IF with ENDIF
Begin loop with LOOP and end with
ENDLOOP
Show MAINLINE first; all others follow
TERMINAE all routines with an END
instruction
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Structured program languages lend
themselves to flowcharts, structure charts,
and pseudocode.
Structured programming languages work
best where the instructions have been
broken up into small, manageable parts.
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Structure charts illustrate the structure of a
program by showing independent hierarchical
steps.
Major divisions are subdivided into smaller
pieces of information.