Download - pseudo code basics
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Pseudocode
• It Means:
• IMITATION or FALSE CODE
• It is an imitation of the computer instruction
• Using this programmer can concentrate on developing logic without worrying about syntax
• Easy to convert into programming language
Writing PseudocodeBasic computer operations
There are six basic computer operations1. computer can receive information2. computer can put out information3. computer can perform arithmetic4. computer can assign a value to a variable or
memory location5. computer can compare two variables and select
one of two alternate actions6. computer can repeat a group of actions
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Six Basic Computer Operations
1 A computer can receive information– When a computer is required to receive
information or input from a particular source, whether it is a terminal, a disk or any other device, the verbs Read and Get are used in pseudocode
Read => Input from a record
Get => Input from keyboard
Example pseudocode
1.Read student name2.Get system data3.Read number1, number24.Get tax_code
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Six Basic Computer Operations
2 A computer can put out information– When a computer is required to supply
information or output to a device, the verbs Print, Write, Put, Output, or Display are used in pseudocode
– Print => send output to printer– Write => send out to file– Put, Output, Display => send
to screen
Example pseudocode1.Print ‘Program Completed’2.Write customer record to master file3.Output total tax4.Display ‘End of data’
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Six Basic Computer Operations
3 A computer can perform arithmetic– Most programs require the computer to perform some sort of
mathematical calculation, or formula, and for these, a programmer may use either actual mathematical symbols or the words for those symbols
– To be consistent with high-level programming languages, the following symbols can be written in pseudocode:+ for Add - for Subtract* for Multiply / for Divide ( ) for Parentheses
– When writing mathematical calculations for the computer, standard mathematical ‘order of operations’ applies to pseudocode and most computer languages
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Six Basic Computer Operations
4 A computer can assign a value to a variable or memory location
– There are three cases where you may write pseudocode to assign a value to a variable or memory location:
1. To give data an initial value in pseudocode, the verbs Initialize 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
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Six Basic Computer Operations
4 A computer can assign a value to a variable or memory location
Example pseudocode
1.Initialize total_price to zero2.Set student_count to zero3.Total_price = cost_price + sales_tax4.Total_price cost_price + sales_tax5.Store customer_num in last_customer_num
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Six Basic Computer Operations
5 A computer can compare two variables and select one or two alternate actions
– An important computer operation available to the programmer is the ability to compare two variables and then, as a result of the comparison, select one of two alternate actions
– To represent this operation in pseudocode, special keywords are used: IF and ELSE
The Selection Structure
amount < 100
interestRate = .06 interestRaate = .10
yes no
1. IF amount < 1001.1 interestRate = .06
2. ELSE2.1 Interest Rate = .10Pseudocode
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Six Basic Computer Operations
6 A computer can repeat a group of actions
– When there is a sequence of processing steps that need to be
repeated, a special keyword, WHILE is used in pseudocode
– The condition for the repetition of a group of actions is
established in the WHILE clause, and the actions to be
repeated are listed beneath it
Repetition using WHILEStart
count = 0
count <10
add 1 tocount
write count
Write“The End”
Stop
1. count = 02. WHILE count < 10
2.1 ADD 1 to count2.2 WRITE count
3. WRITE “The End”
Mainline
1.count = 0
2.DOWHILE count < 10
2.1 DO Process
3.WRITE “The End”
Process
2.1 ADD 1 to count
2.2 WRITE count
Modular
Rules for Pseudocode
• Write only one statement per line
• Capitalize initial keyword
• Indent to show hierarchy
• End multiline structures
• Keep statements language independent
One Statement Per Line
Each statement in pseudocode should express just one action for the computer.
PseudocodeREAD name, hoursWorked, payRate
gross = hoursWorked * payRate
WRITE name, hoursWorked, gross
Capitalize Initial Keyword
In the example below note the words: READ and WRITE. These are just a few of the keywords to use, others include:
READ, WRITE, IF, ELSE, ENDIF, WHILE, ENDWHILE
Pseudocode
READ name, hoursWorked, payRate
gross = hoursWorked * payRate
WRITE name, hoursWorked, gross
Rules for Variable Names
• Begin with lowercase letter
• Contain no spaces
• Additional words begin with capital
• Unique names within code
• Consistent use of names
Indent to Show Hierarchy
• Sequence: Keep statements in sequence all starting in the same column
• Selection:Indent statements that fall inside selection structure, but not the
keywords that form the selection
• Loop:Indent statements that fall inside the loop but not keywords that
form the loop
Each design structure uses a particular indentation pattern
READ name, grossPay, taxes
IF taxes > 0
net = grossPay – taxes
ELSE
net = grossPay
ENDIF
WRITE name, net
End Multiline Structures
See the IF/ELSE/ENDIF as constructed above, the ENDIF is in line with the IF.
The same applies for WHILE/ENDWHILE etc…
READ name, grossPay, taxes
IF taxes > 0
net = grossPay – taxes
ELSE
net = grossPay
ENDIF
WRITE name, net
Types of Logic Structure
• Sequence
• Selection
• Iteration
Sequence
• Performing instruction one after another
The Selection Structure
amount < 100
interestRate = .06 interestRate = .10
yes no
IF amount < 100
interestRate = .06
ELSE
Interest Rate = .10
ENDIF
Pseudocode
The Looping Structure
In flowcharting one of the more confusing things is to separate selection from looping. This is because each structure use the diamond as their control symbol. In pseudocode we avoid this by using specific keywords to designate loopingWHILE/ENDWHILE
REPEAT/UNTIL
WHILE / ENDWHILEStart
count = 0
count <10
add 1 tocount
write count
Write“The End”
Stop
count = 0
WHILE count < 10
ADD 1 to count
WRITE count
ENDWHILE
WRITE “The End”
Mainline
count = 0
WHILE count < 10
DO Process
ENDWHILE
WRITE “The End”
Process
ADD 1 to count
WRITE count
Modular
REPEAT / UNTILStart
count = 0
count <10
add 1 tocount
write count
Write“The End”
Stop
count = 0
REPEAT
ADD 1 to count
WRITE count
UNTIL count >= 10
WRITE “The End”
Mainline
count = 0
REPEAT
DO Process
UNTIL count >= 10
WRITE “The End”
Process
ADD 1 to count
WRITE count
Modular
Advantages & Disadvantages
Flowchart Advantages: Standardized Visual
Pseudocode Advantages Easily modified Implements structured
concepts Done easily on Word
Processor
Flowchart Disadvantages: Hard to modify Structured design elements not
implemented Special software required Time Consuming
Pseudocode Disadvantages: Not visual No accepted standard, varies from
company to company
Working with Fields
Calculations
+ add
- subtract
* multiply
/ divide
** or ^ exponentiation
( ) grouping
Selection
> greater than
< less than
= equal to
>= greater than or equal to
<= less than or equal to
!= not equal to
Any Questions