DCT 1123 Problem Solving & AlgorithmsPseudocode & Flowchart

Con

tents

• How to write a pseudocode• Meaningful names• The structure theorem• Flowchart

SIX

basic co

mpu

ter

opera

tion

1. A computer can receive information

2. A computer can put out information3. A computer can perform arithmetic4. A computer can assign a value to a

variable or memory location5. A computer can compare two

variable and select one of two alternative actions

6. A computer can repeat a group of actions

Rece

ive In

form

atio

n

• When computer is required to receive information or input from a particular source, whether it be a terminal, a disk or any other device

• ‘Read’ and ‘Get’ are used in the pseudocode

• Read – receive input from a record/file

• Get – receive input from keyboard

Rece

ive In

form

atio

n

• For example:Read student nameGet system dateRead number1, number2Get tax code

Pu

t Ou

t Info

rmatio

n

• When a computer is required to supply information or output to a device, the verbs Print, Write, Output or Display are used

• Print – output is sent to the printer• Write – output is to be written to a

file• Put, Output and Display – output is

to be written to the screen

Pu

t Ou

t Info

rmatio

n

• For example:– Print ‘Program Completed’– Write customer record to master file– Put out name, address and postcode– Output total_tax– Display ‘End of Data’

Perfo

rm A

rithm

etic

• Most programs require the computer to perform some sort of mathematical calculation and apply a formula

• The following symbols can be written in pseudocode:– + for add– - for substract– * for multiply– / for divide– () for parantheses

• The verbs ‘Compute’ and ‘calculate’ also used in the pseudocode

Perfo

rm A

rithm

etic

• For example:– Divide total marks by student_count– Sales_tax = cost_price * 0.10– Compute C = (F – 32) * 5 / 9

Assig

n a

valu

e to

a

varia

ble

/ mem

ory

loca

tion

• There are 3 instances in which you may write a pseudocode to assign a value to a variable / 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

Assig

n a

valu

e to

a

varia

ble

/ mem

ory

loca

tion

• For example:– Initialize total_price to zero– Set student_count to 0– Total_price = cost_price + sales_tax– Total_price cost_price + sales_tax– Store customer_no in last_customer_no

Com

pare

two v

aria

ble

s & se

lect

on

e o

r two a

ltern

ativ

e a

ction

• To represent this operation in pseudocode, special keywords are used: IF, THEN and ELSE

• The comparison of data is established in the IF clause

• The choice of alternatives is determined by the THEN or ELSE

Com

pare

two v

aria

ble

s & se

lect

on

e o

r two a

ltern

ativ

e a

ction

• For example:

IF attendance_status is part_time THENAdd 1to part_time_count

ELSEAdd 1 to full_time_count

ENDIF

Repeat a

gro

up

of a

ction

• When there is a sequence of processing steps that need to be repeated, two special keywords, DOWHILE and ENDDO are used in pseudocode

• The repetition condition is established in the DOWHILE clause and the actions to be repeated are listed beneath it

Repeat a

gro

up

of a

ction

• For example:

DOWHILE student_total < 50Read student recordPrint student name, address to reportAdd 1 to student_total

ENDDO

Mean

ing

ful N

am

es

• A programmer must introduce some unique names, which will be used to represent the variables or objects in the problem

• A name given to a variable is simply a method of identifying a particular storage location in the computer

• A name describes the type of data stored in a particular variable

• A variable may be one of three simple data types: an integer, a real number or a character

Mean

ing

ful N

am

es

• If more than one word is used in the variable name, the underscores are useful as word separator. For example student_number

• If underscore cannot be used, then words can be joined together with the use of a capital letter as a word separator. For example studentNumber

Flo

wch

art

• Flowchart is an alternative method of representing algorithms

• It is popular because they graphically represent the program logic through series of standard geometric symbols and connecting lines

Flo

wch

art S

ym

bols

Terminal SymbolIndicates the starting or stopping point in the logic. Every flowchart should begin and end with a terminal symbol.

Input / Output SymbolRepresents an input or output process in an algorithm, such as reading input or writing output

Flo

wch

art S

ym

bols

Process SymbolRepresents any single process in an algorithm, such as assigning a value or performing a calculation

Predefined Process SymbolRepresents an input or output process in an algorithm, such as reading input or writing output

Flo

wch

art S

ym

bols

Decision SymbolRepresents a decision in the logic involving the comparison of two values. Alternative paths are followed, depending on whether the decision symbol is true or false

FlowlinesConnect various symbols in a flowchart, and contain an arrowhead only when the flow control is not from top to bottom or left to right

Flow

chart C

ontro

l Stru

cture

• There are three basic control structures:1. Sequence

• Straightforward execution of one processing step after another

2. Selection• Presentation of a condition, and the choice

between two actions depending on whether the condition is true or false

3. Repetition• Presentation of a set of instructions to be

performed repeatedly, as long as condition is true

Flow

chart C

ontro

l Stru

cture

• Sequence flowchart example:

Statement A

Statement C

Input / Output

Flow

chart C

ontro

l Stru

cture

• Selection flowchart example

Condition p?

Statement A Statement B

True False

Flow

chart C

ontro

l Stru

cture

• Repetition Flowchart Example

Condition p?

Statement A

True

False

Su

mm

ary

• Six basic computer operations were listed – receive information, put out information, perform arithmetic, assign a value o a variable, decide between two alternative actions and repeat a group of actions

• The algorithm can be represented in the pseudocode or flowchart