Transcript Introduction to Pseudocode - Jurusan Teknik Elektro dan

TEL 104 / MKK
Fundamental Programming:
Lecture 3
1
Assignment 1 Review:
• A program is required to read from
the screen the lenght and widht of
a rectangular house block, and the
lenght and width of the rectangular
house that has been built on the
block. The algorithm should then
compute and display the mowing time
required to cut the grass around
the house, at the rate of two
square metres per minute
Step 1
• A program is required to read from
the screen the lenght and widht of
a rectangular house block, and the
lenght and width of the rectangular
house that has been built on the
block. The algorithm should then
compute and display the mowing time
required to cut the grass around
the house, at the rate of two
square metres per minute.
• Defining diagram
Input
Block_lenght
Block_width
House_lenght
House_width
Processing
Output
Mowing_time
Step 2
• A program is required to read from
the screen the lenght and widht of
a rectangular house block, and the
lenght and width of the rectangular
house that has been built on the
block. The algorithm should then
compute and display the mowing time
required to cut the grass around
the house, at the rate of two
square metres per minute.
• Defining diagram
Input
Block_lenght
Block_width
House_lenght
House_width
Processing
Prompt for block measurements
Get block measurements
Prompt for house measurements
Get house measurements
Calculate mowing area
Calculate mowing time
Output
Mowing_time
Introdution to Program Data
Three main discussion:
– Variables
– Constants
– Literals
Variables
– Is the name given to a collection of memory
cell, designed to store particular data item.
– The value stored may change or vary as the
program executes.
– Example: variable total_amount  may
contain several values during the execution of
the program
Constant
• Is a data item with a name and a value
that remain the same during the execution
of the program.
• Example : name: ´´Fifty´´  given to a
data item that contains the value 50
Literal
• Is a constant whose name is the written
representation of its value.
• Example: the program may contain the
literal `50`
Data Types
• Should be clearly defined at the beginning
of the program.
• Can be:
• Elementary data items
• Data structures
Elementary data items
• Contain single variable that is always
treated as a unit.
• Usually classified into data types.
• A data type consists of a set of data values
and a set of operation that can be
performed on those values.
Elementary data Items (cont)
The most common elementary data types:
1. Integer: representing a set of whole numbers,
positive, negative or zero.
e.g. 3, 576, -5
2. Real : representing a set of numbers, positive or
negative, which may include values before or after a
decimal point. Sometimes referred to as floating
point numbers.
e.g. 19.2, 1.92E+01, -0.01
The most common elementary data types: (cont)
3. Character: representing the set of
characters on the keyboard, plus some
special characters.
e.g. ´A´, `b`, ´$´
4. Boolean: representing a control flag or
switch, which may contain one of only
two possible values; true or false.
Data Structures
• Is an aggregate of other data items.
• Its component could be elementary data
items or another data structure.
• Data is grouped together in a particular
way to reflects the situation with which the
program is concerned.
The most common Data Structures:
• Record: a collection of data items or fields
that all bear some relationship to one
another.
example: a student record  may contain
the student‘s number, name, address and
enrolled subjects.
• File: a collection of records.
example: a student file  may contain a
collection of the above student records.
The most common Data Structures:
(cont)
•
Array: a data structure that is made up of a
number of variables or data items that all have
the same data type and are accessed by the
same name.
Example: an array called ´scores´ may
contain a collection of students‘ exam scores.
Access to the individual items in the array is
made by the use of an index or subscript
beside the name of the array  scores[3]
The most common Data Structures: (cont)
• String: a collection of characters that can
be fixed or variable.
Example: the string ´Basnendar Eko´may
represent a student‘s name.
Files
• A popular method to enter and store
information.
• Major advantage of using files are:
– Several different program can access the
same data
– Data can be entered and reused several
times.
– Data can be easily updated and maintained.
– The accuracy of the data is easier to enforce.
Files (cont)
• Two different methods of storing data on
files:
– Sequential or text files, where data is stored
and retrieved sequentally  may be opened
to read or to write, but not both operations on
the same file.
– Direct or random-access files, where data is
stored and retrieved randomly, using a key or
index  can be opened to read and write on
the same file.
Data Validation
• Data should always undergo a validation check
before it is processed by a program.
• Different types of data require different check –
for example:
– Correct type: the input data should match the data
type definition stated at the beginning of the program.
– Correct range: the input should be within a required
set of values.
– Correct lenght: the input data – for example, string –
should be the correct length.
– Completeness: all required fields should be present.
– Correct date: an incoming data should be acceptable.
Introduction to Pseudocode
What is Pseudocode?
• One of the popular representation of
Algorithm
• Widely choosen because:
– easy to read and write
– allow the programmer to concentrate on the
logic of the problem
– Structured in English language
Pseudocode Convention
• Statement are written in simple English
• Each instruction is written on a separate line
• Keywords and indentation are used to signify
particular control structures.
• Each set of instructions is written from top to
bottom, with only one entry and one exit.
• Groups of statements may be formed into
modules, and that group given a name.
Six Basic Computer Operations
1.
A computer can receive information
Verb used:
•Read  used when the algorithm is to receive the input from a record on a file
•Get  used when the algorithm is to receive input from the keyboard.
Read student name
Get system date
Read number_1,
number_2
Get tax_code
2. A computer can put out information
Verb used:
•Print  used when the output is to be sent to the printer
•Write  used when the output is to be written to a file
•Put, Output, Display  used when the output is to be written to the screen
•Prompt  required before an input instruction Get, causes the message to be
sent to the screen which requires the user responds, usually by providing input.
Print `Program Completed´
Write customer record to master file
Put out name, address and postcode
Output total_tax
Display ´End of data´
Prompt for student_mark
Get student_mark
3. A computer can perform arithmetic
Verb used:
•Compute
•Calculate
•Symbols used:
+, -, *, /, ()
Add number to total
Total = total + number
Divide total_marks by student_count
Sales_tax = cost_price * 0.10
Compute C = (F – 32) * 5/9
4.
•
A computer can assign a value to a variable
or memory location
Three cases :
1. To give data an initial value in pseudocode, the
verbs Initialise or Set are used
2. To assign a value as a result of some processing,
the symbols ´=´or ´´ are written
3. To keep a variable for later use, the verbs Save or
Store are used.
Initialize total_price to zero
Set student_count to 0
Total_price = cost_price + sales_tax
Total_price  cost_price + sales_tax
Store customer_num in last_customer_num
5.
A computer can compare two variables and
select one of two alternate actions
Keyword used:
IF, THEN, ELSE
IF student_attendance_status is
part_time THEN
add 1 to part_time_count
ELSE
Add 1 to full_time_count
ENDIF
6. A computer can repeat a group of actions
Keyword used:
DOWHILE, ENDDO
DOWHILE student_total < 50
Read student record
Print student name, address to report
Add 1 to student_total
ENDDO
Meaningful names
• When designing a solution algorithm, a
programmer should introduce unique names,
which are:
– Represent the variables or objects in the problem
– Meaningful
example: number1, number2, number3  more
meaningful than A, B, C
- Used word separator if more than one word
example: sales_tax, word_count
- Or Capital letter as separator
example: salesTax, wordCount
The Structure Theorem
• It is possible to write any computer
program by using only three basic control
structures that are easily represented in
pseudocode:
»Sequence
»Selection
»Repetition
Sequence
Is the straightforward execution of one processing step after another.
Statement a
Statement b
Statement c
•
•
•
•
•
Add 1 to pageCount
Print heading line 1
Print heading line 2
Set lineCount to zero
Read customer record
Selection
Presentation of condition and the choice between two actions
IF condition p is true THEN
statement(s) in true case
ELSE
statement(s) in false case
ENDIF
Example:
IF student_attendance_status is part_time THEN
add 1 to part_time_count
ELSE
add 1 to full_time_count
ENDI>f
Repetition
The presentation of a set of instructions to be performed repeatedly,
as long as a condition is true
DOWHILE condition p is true
statement block
ENDDO
Example:
Set student_total to zero
DOWHILE student_total < 50
Read student record
Print student name, address to report
Add 1 to student_total
ENDDO
DESIGNING A SOLUTION ALGORITHM
• The most challengin task in the life cycle
of a program
• First attempt usually doesnt result in a
finished product
• Keep altering the step and algorithms till
satesfied result achieved.
Point to be considered in Solution Algorithm
1. A name should be given to the algorithm,
which is describe the function of algorithm
2. An END statement used to indicate the
algorithm is complete
3. All processing steps between the algorithm
name and END statement should be indented
for readability.
4. Each processing step in the defining diagram
relates directly to one or more statements in
the algorithm.
Example 3.1. Solution Algorithm for example 2.1

A program is required to read
three numbers, add them
together and print their
total.
• Defining diagram
Input
Number1
Number2
Number3
Processing
Output
total
Solution Algorithm
• Add_three_numbers
Read number1, number2, number3
Total = number1 + number2 + number3
Print total
END
Example 3. 2. Find average temperature
• A program is required to prompt the
terminal operator for the maximum
and minimum temperature readings on
a particular day, accept those
readings as integers, and calculate
and display to the screen the
average temperature, calculated by
(maximum temperature + minimum
temperature)/2.
• Defining diagram
Input
Max_temp
Min_temp
Processing
Output
Prompt for temperatures
Avg_temp
Get temperatures
Calculate average temperature
Display average temperature
Solution Algorithm
• Find average_temperature
Prompt operator for max_temp, min_temp
Get max_temp, min_temp
Avg_temp= (max_Temp + min_temp)/2
Output avg_temp to the screen
END
What about this ? Compute mowing time
• A program is required to read from
the screen the lenght and widht of
a rectangular house block, and the
lenght and width of the rectangular
house that has been built on the
block. The algorithm should then
compute and display the mowing time
required to cut the grass around
the house, at the rate of two
square metres per minute.
Solution Algorithm
Calculate_mowing_time
Prompt operator for block_lenght, block_width
Get block_length, block_width
block_area = block_lenght*block_width
Prompt operator for house_lenght, house_width
Get house_lenght, house_width
house_area=house_lenght*house_width
Mowing_area=block_area-house_area
Mowing_time=mowing_area/2
Output mowing_time to screen
END
Checking the solution algorithm
(Desk Checking)
• Tracing through the logic of the algorithm
with some chosen data..
Step in desk Checking an algorithm
1. Choose valid simple input test case (2-3
enough)
2. Establish what the expected result should be.
3. Make a table of relevant variable names
4. Checking the test case line by line, step by
step
5. Repeat process 4 for other test case
6. Check if expected result 2 matches with actual
result 5
Example 3.4. Desk Chek for example 2.1

A program is required to read
three numbers, add them
together and print their
total.
Solution Algorithm
• Add_three_numbers
Read number1, number2, number3
Total = number1 + number2 + number3
Print total
END
Desk Checking
1. Choose two sets input test data.
Set 1: 10,20, 30 and Set 2: 40, 41, 42
Data Set 1
Data Set 2
Number 1
10
40
Number 2
20
41
Number 3
30
42
2. Establish the expected result for each test case
Total
Data Set 1
Data Set 2
60
123
3. Set up a table of relevant variable names, and
pass each test data set statement by statement.
Statement
number
number1
number2
number3
10
20
30
total
First Pass
1
2
60
3
Print
Second
Pass
1
40
41
42
2
123
3
Print
4. Check the expected results (60 and 123) match
the actual results.
Desk Check of Example 3. 2.
• A program is required to prompt the
terminal operator for the maximum
and minimum temperature readings on
a particular day, accept those
readings as integers, and calculate
and display to the screen the
average temperature, calculated by
(maximum temperature + minimum
temperature)/2.
Solution Algorithm
• Find average_temperature
Prompt operator for max_temp, min_temp
Get max_temp, min_temp
Avg_temp= (max_Temp + min_temp)/2
Output avg_temp to the screen
END
Desk Checking
1. Choose two sets input test data.
Set 1: 30, 10 and Set 2: 40, 20
Data Set 1
Data Set 2
Max_temp
30
40
Min_temp
10
20
2. Establish the expected result for each test case
Avg_temp
Data Set 1
Data Set 2
20
30
3. Set up a table of relevant variable names, and
pass each test data set statement by statement.
Statement
number
Max_temp
Min_temp
30
10
Avg_temp
First Pass
1,2
3
20
4
0utput
Second Pass
1,2
40
20
3
30
4
output
4. Check the expected results match the actual
results.
Assignment 2:
Desk Checking for
Compute mowing time
• A program is required to read from
the screen the lenght and widht of
a rectangular house block, and the
lenght and width of the
rectangular house that has been
built on the block. The algorithm
should then compute and display
the mowing time required to cut
the grass around the house, at the
rate of two square metres per
minute.
Solution Algorithm
Calculate_mowing_time
Prompt operator for block_lenght, block_width
Get block_length, block_width
block_area = block_lenght*block_width
Prompt operator for house_lenght, house_width
Get house_lenght, house_width
house_area=house_lenght*house_width
Mowing_area=block_area-house_area
Mowing_time=mowing_area/2
Output mowing_time to screen
END
Assignment 3 – Desk Checking for Mowing_time which
now contains a logic error
Calculate_mowing_time
Prompt operator for block_lenght, block_width
Get block_length, block_width
block_area = block_lenght * block_width
Prompt operator for house_lenght, house_width
Get house_lenght, house_width
house_area=block_lenght * block_width
Mowing_area=block_area - house_area
Mowing_time=mowing_area/2
Output mowing_time to screen
END
Rule of Assignment Submission
• Submit at the latest one day before the
following class begin.
• Submission after the time will be
considered as delay and affect the mark.
• Use a combination of your name and
assignment number as file name.
• For example:
BasnendarE_Assigment1.doc