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INTRODUCTION TO
PROGRAMMING STRUCTURE
Chapter 4
Overview
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Pointers
Modules & Functions
Cohesion & Coupling
Local & Global Variables
Parameters
Variable Names & Data Dictionaries
Three Logic Structures
Pointers for Structuring a program
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
Use Modules
 Each

part should have a particular function
Use the four logic structures
 Sequential


, Decision , loop & case
Eliminate the rewriting of identical processes by
using modules .
Use techniques to improve readability.
Pointers for Structuring a program
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- The computer should be a tool to help people find
solutions to their problems and to increase their
productivity.
- You can develop efficient computer solutions to
problems if you heed the following pointers:
1- Use modules. Break the whole into parts, each part
having a particular function.
Pointers for Structuring a program
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2- Use the four logic structures to ensure that solution flows
smoothly from one instruction to the next, rather than jumping
from one point in the solution to another.
a- The sequential structure executes instructions one
after another in a sequence.
b- The decision structure branches to execute one of
two possible sets of instructions.
c- The loop structure executes a set of instructions
many times.
d- The case structure executes one set of instructions
out of several sets.
Sequential Logic Structure
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Decision Logic Structure
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Loop Logic Structure
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Case Logic Structure
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rules for designing modules

Each module
 is
an entity by itself . There is one entrance and one
exit , the processing does not jump out of the middle of
a module to another module.
 has a single function ( printing , calculating , entering
data)
 should be easily read, modified ( short enough).
 Length is governed by function and number of
instructions contained within
 Controls the order of processing.
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Types of modules
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Control modules .
Initialization module
Process module ( process only once or loop):
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
calculation modules .
print modules .
read and data validation modules.
Wrapup modules
Control Modules
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Most often called “Main”
shows the overall flow of the data through the
program
All other modules are subordinate to the control
module.
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Initialization Module
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that are executed only once during the program
and only at the beginning.
 Examples
 Opening
files
 Initializing variables ( beginning values )
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Process Modules

May be processed only once , or the may be part of
a loop , there are several kind :
 Calculation
modules:
 arithmetic
operations
 Accumulations
 Counting
 Manipulate string data.
 Read
and Data Validation modules:
 Reads

 Print

and validates input data
Usually separate modules
modules :
print output line( the result of the processing)
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Wrap Up Module

process all instructions that are executed once
during the program and only at the end
 Examples
 Closing
files
 Printing totals .
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Modules
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
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Modules are often combined in one solution .
A module can be broken into several smaller
modules to make the parts of a program more
manageable.
One module performing a specific function can be
used by one or more other modules .
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COHESION & COUPLING
chapter 4
Cohesion & Coupling
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
Each module should
 Be
functionally independent.
 Perform single task .
 Modules will need to connected ,primarily through the
data needed to complete the specified task within the
modules ( cohesion and coupling ) .
cohesion
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
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The ability for a module to work independently
from all other modules ( single entry and single
exit).
Each module should have a function .
Each module should have single entry and single
exit.
coupling
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modules need to share data from other modules in
order to complete the modular tasks.
is accomplished by some type of interface between
modules that enables data to be passed from one
module to another with the minimum interruption of
the modular independence .
Allows for the communication between modules.
There are three ways to couple modules : global
variable , parameters , and return value .
LOCAL AND GLOBAL VARIABLES
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Programmer use the concept of local and global
variables to allow cohesion and coupling to occur.
Global variable( define outside individual module)
Local variables ( define within module)
The difference between the two is in the scope of
the variables .
Local variables
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May be used only by the module itself.
Other modules have no knowledge of these
variables.
Allow cohesion to take place .
The programmer does not have to worry about
variable name duplication in modules created by
other programmers.
The modules can be coupled through the use of
parameters or return values.
global variables
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
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thy can be seen by all modules.
Allow data coupling through the entire program .
The programmer must be careful not to use the
same variable name for local variable and a
global variable .
The use of parameter and return value is not
necessary since global variable couple the data
from module to module .
global variables

Can be referenced anywhere in the program
 Is visible and accessible everywhere
A
X, Y, Z
C
B
X, Y & Z are Global
to modules A, B & C
Interactivity chart
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Scope of Local and Global Variables
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Parameters
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Local variables that are passed from one module to
another .
Another way of coupling that allow the communication
of data between modules.
Thy are placed after module name between
parentheses.
Read ( A , B , C)
Parameters
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
Make modules more versatile.
 Different
data can be manipulated each time the
module is called.

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The calling module (module that process another
module)
The called module ( the module being processed).
Parameter Terminology
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Parameters
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
Parameters Comes in two types:
 Actual
(is the list of parameter that follows the module
name being processed in the calling module )
 Formal (is the list of parameter that follows the module
name at the beginning of the module ).
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The variable name in the actual may or may not be the
same as those in the formal parameter .
The value are sent and received according to the
position in the listings .
Actual & Formal Parameters
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
Actual Parameters
 Parameters
used in the call statement
 Data types must be assignment compatible with its
corresponding formal parameter
 Can be a variable, constant or an expression
 Can be call-by-value or call-by-reference

Formal Parameters
 Must
be a variable
 Can be call-by-value or call-by-reference
Calling data through the modules

There are two ways to send data from one module
to another:
 Send
the value of the variable ( call-by-value)
 Send the address of the variable (call-by-reference)
 Specified
by the use of an asterisk (*) in front of the
variable name ( actual and formal parameter)
Call-by-Reference
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
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the memory location is sent ( the address)
Is specified by the use of an asterisk( * ) in front of
the variable name in both the actual and formal .
Gives access to the contents of the storage area
where values are stored.
When the called module change the value of the
parameter , the calling module will see the change.

They are using the same memory location.
Call-by-Value
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the value of the variable is sent to the called module
by the calling module.
Accomplished by creating a copy of the value
The called module will make a new memory location
for this variable .
When the called module makes a change in the
variable ,the change will not be made in the calling
module.

Parameter have different memory location
Parameters – Call-by-value and Call-byReference
Parameters – Call-by-value and Call-byReference
Parameters – Call-by-value and Call-byReference
Parameter Example
Coupling diagram
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A coupling diagram indicates how data couples
modules together
Has a rectangle for each module .
Line connecting the modules for each datum sent
from one module to another .
The double-headed arrows indicate that these
parameters are call - by - reference .
The single- headed arrows indicate that these
parameters are call-by-value .
Coupling diagram
Coupling diagram
parameters
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Parameter in the formal parameter listing are neither
local nor global variables .
Should not be declared as local or global variables.
In the event of variable name duplication , the local
variable has precedence over the parameter
variable .
The parameter variable has precedence over the
global variables .
Return value
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Another way to couple modules .
The return value is the result of the function .
This is accomplished through the name of the function.
The result is placed temporarily in the name.
The function must be used as parts of another
instruction.
SquareRoot = 5 + SQRT ( 16 )

The value of SQRT is no longer available to be used
Variable Names and the data dictionary
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Use a variable name that relates the name of the
variable to its usage.
Variable name must be unique to the module in thy
are defined.
Global variable must be unique to the total
program .
The computer references values by their names .
Data dictionary is a great help to keep track of the
variable usage in your program .And Defines all of
the variables used within a program.
Example of a Data Dictionary
The four Logic Structures
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

control the logic of the data flow through the
module.
The four basic logic structures :
 Sequential
logic structure
 Decision logic structure .
 Loop logic structure .
 Case logic structure .