tugas progdas 02 - developing an algorithm

8/6/2019 TUGAS PROGDAS 02 - Developing an Algorithm

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CHAPTER 3 :

DEVELOPINGANALGORITHM

Muh Anung Darmawan 33209

Muhammad Muzani 33267


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DEFINING THE PROBLEM (1)

To help with the initial analysis, the problem

should be divided into three separate

components:

1. Input: a list of the source data provided to theproblem.

2. Output: a list of the outputs required.

3. Processing: a list of actions needed to produce the

required outputs.


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EXAMPLE : Add three numbers

1. Tackle this problem in two stages. First, underline the

nouns and adjectives used in the specification. We get

2. By looking at the underlined nouns and adjectives,

you can see that the input for this problem is threenumbers and the output is the total. It is helpful to

write down these first two components in a simple

diagram, called a defining diagram.


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3. Then, underline the verbs and adverbs used in thespecification. This will establish the actions required. We get:

4. By looking at the underlined words, we can see that theprocessing verbs are 'read', 'add together' and 'print'. We geta complet defining diagram :

When we get a complete defining diagram, the problem hasbeen properly defined. That is, we now understand the inputto the problem, the output to be produced, and the processingsteps required to convert the input to the output.


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When it comes to writing down the processing steps in

an algorithm, you should use words that describe thework to be done in terms of single, specific tasks or

functions. For example:

There is a pattern in the words chosen to describe these

steps. Each action is described as a single verb followed

by a two-word object. Studies have shown that if you

follow this convention to describe a processing step,

two benefits will result. First, you are using a disciplinedapproach to defining the problem; and second, the

processing is being divided into separate tasks or functions.

This simple operation of dividing a problem into separate

functions and choosing a proper name for each function is

extremely important later, when considering algorithm

modules.


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DESIGNING A SOLUTION ALGORITHM (1)

it is important that we are not too anxious to

start coding until the necessary steps of

defining the problem and designing the

solution algorithm have been completed. Here are solution algorithm for the preceding

example. It involve sequence control structures

only; there are no decisions or loops, so the

solution algorithms are relatively simple.


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Example : Solution algorith for last example

This diagram shows what is required, and a simple calculation

will establish how. Using pseudocode, and the sequence controlstructure, establish the solution algorithm as follows:


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There are a number of points to consider in this solution

algorithm:

1. Aname has been given to the algorithm, namely

Add_three_numbers. Algorithm names should briefly describe the

function of the algorithm, and are usually expressed as a single

verb followed by a two-word object.

2. An END statement at the end of the algorithm indicates that the

algorithm is complete.

3. All processing steps between the algorithm name and the END

statement have been indented for readability.

4. Each processing step in the defining diagram relates directly to oneor more statements in the algorithm. For instance, 'Read three

numbers' in the defining diagram becomes 'Read number1,

number2, number3' in the algorithm; and 'Add number together'

becomes 'total = number1 + number2 + number3'.

Now that the algorithm is complete, we should desk check the

solution and then translate it into a programming language.


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CHECKING THE SOLUTION ALGORITHM

(1)

After a solution algorithm has been established,

it must be tested for correctness. This step is

necessary because most major logic errors occur

during the development of the algorithm, and if

not detected, these errors can be passed on to the

program


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(2)

Selecting test data

y By doing this, we will still be able to concentrate on

what the program is supposed to do, not how.

Steps in desk checking an algorithm1. Choose simple input test cases that are valid.

Two or three test cases are usually sufficient.

2. Establish what the expected result should be for

each test case

3. Make a table on a piece of paper of the relevantvariable names within the algorithm


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(3)

4. Walk the first test case through the algorithm,

line by line, keeping a step-by-step record of the

contents of each variable in the table as the data

passes through the logic.

5. Repeat the walk-through process using theother test data cases, until the algorithm has

reached its logical end.

6. Check that the expected result established in

Step matches the actual result developed in Step 5.


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(4)

By desk checking an algorithm, you are

attempting to detect early errors.

Desk checking will eliminate most errors, but it

still cannot prove that the algorithm is 100%correct!

Bellow is an example of desk checking

(meskipun hanya 4 langkah, tetapi contoh

tersebt telah melewati 6 langkah yang telah

dijelaskan di 2 slide sebelum ini) :


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(5)

We have :

1. We input 2 data set, we get :

2. We calculate the 2 input data set, we 2 set output :


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(6)

3. Set up a table of relevant variable names, and pass

each test data set through the solution algorithm,

statement by statement. Line numbers have been

used to identify each statement within the program.


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(7)

4. Check that the expected results (60 and 123) match

the actual results (the total column in the table).

This desk check, which should take no more than a few

minutes, indicates that the algorithm is correct. You can

now proceed to code the algorithm into a programminglanguage.Note that if, at the end of a desk check, the

actual results do not match the expected results, the

solution algorithm probably contains a logic error. In this

case, the programmer needs to go back to the solution

algorithm, fix the error, then desk check the

algorithm again.


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THEEND

tugas progdas 02 - developing an algorithm

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