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5.4 Modular Design

• Top-Down Design

• Structured Programming

• Advantages of Structured Programming

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Design Terminology

• Large problems can be broken down into smaller problems

• divide-and-conquer approach called stepwise refinement

• Stepwise refinement is part of top-down design methodology

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Top-Down Design

• General problems are at the top of the design

• Specific tasks are near the end of the design

• Top-down design and structured programming are techniques to enhance programmers' productivity

Top-down design aided through the use of hierarchy charts

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Top-Down Design Criteria1. The design should be easily readable and

emphasize small module size.2. Modules proceed from general to specific as you

read down the chart.3. The modules, as much as possible, should be

single minded. That is, they should only perform a single well-defined task.

4. Modules should be as independent of each other as possible, and any relationships among modules should be specified.

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Beginning of Hierarchy Chart

Start by determining the high-level tasks

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Detailed Hierarchy Chart

Then refine the major tasks, breaking them

into subtasks.

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Structured Programming Control structures in structured programming:• Sequences: Statements are executed one

after another.• Decisions: One of two blocks of program code

is executed based on a test of a condition.• Loops (iteration): One or more statements are

executed repeatedly as long as a specified condition is true.

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Advantages of Structured Programming

Goal to create correct programs that are easier to

• write

• understand• modify

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Easy to Write

• Allows programmer to first focus on the big picture and take care of the details later

• Several programmers can work on the same program at the same time

• Code that can be used in many programs is said to be reusable

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Easy to Debug

• Procedures can be checked individually

• A driver program can be set up to test modules individually before the complete program is ready.

• Using a driver program to test modules (or stubs) is known as stub testing.

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Easy to Understand

• Interconnections of the procedures reveal the modular design of the program.

• The meaningful procedure names, along with relevant comments, identify the tasks performed by the modules.

• The meaningful procedure names help the programmer recall the purpose of each procedure.

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Easy to Change

• Because a structured program is self-documenting, it can easily be deciphered by another programmer.

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Object-Oriented Programming

• an encapsulation of data and code that operates on the data

• objects have properties, respond to methods, and raise events.

5.5 Case Study

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Validate and input

data

Compute current

earnings

Compute total

earnings to date

Compute FICA tax

Compute income tax

withheld

Compute take-home

pay

Display info

Adjust pay by

withholding allowances

Withheld (single)

Withheld (married)

Give payroll information

5.5 Case Study

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5.5 Case Study

The major steps in the high-level

task of displaying the payroll information are found in

the event procedure.

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5.5 Case Study

Statements calling the

procedures for Task 0 (validating

and inputting

data).

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5.5 Case Study

Statement calling the procedure for Task 1 (computing

current earnings).

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5.5 Case Study

Statement calling the procedure for Task 2 (computing

total earnings to

date).

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5.5 Case Study

Statement calling the procedure for Task 3 (computing FICA tax).

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5.5 Case Study

Statement calling the procedure for Task 4 (computing income tax withheld).

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5.5 Case Study

Statement calling the procedure for Task 5 (computing take-home

pay).

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5.5 Case Study

Statement calling the procedure for Task 5 (displaying

information).

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5.5 Case Study

Procedures for Task 0 (validating

and inputting

data).

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5.5 Case Study

Procedure for Task 1 (computing

current earnings).

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5.5 Case Study

Procedure for Task 2 (computing

total earnings to

date).

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5.5 Case Study

Procedure for Task 3 (computing FICA tax).

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5.5 Case Study

Procedure for Task 4 (computing income tax withheld).

Task 4 involves

three subtasks.

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5.5 Case Study

Procedures for Tasks 4.2 (single withholding) and 4.3 (married withholding).

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5.5 Case Study

Procedure for Task 5 (computing take-home

pay).

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5.5 Case Study

Procedure for Task 5 (displaying

information).

Stub Testing• A stub is an empty procedure.

• You can create functions or procedures with mainly just the signature and a minimum bit of code

• Thus, the whole calling process can be tested before testing the individual modules

• That way, you can incrementally build the application, one module at a time.

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Stub Testing

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Here, the tasks are

implemented as procedure

stubs.

Stubs have very little code inside, mainly

just the signatures.

Stub Testing

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Note: for Function stubs,

you need something for a return value…here we just

arbitrarily return 0.

This program will compile, and you can test to ensure that the proper procedures are being called.

Running program outside VB.net

• Distribution program (not files) to others:• 1 file• No ability to edit• Must have Microsoft’s .NET Framework

• Most computers have (it is free)

• Change icon• Set startup form• Choose the Debug/Build menu option• .EXE file is Located in bin\Release folder

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