Read ......http://faculty.ccri.edu/mkelly/COMI1150/PseudocodeBasics.pdf

Then create pseudocode based on this page.

Pseudocode: An Introduction

Flowcharts were the first design tool to be widely used, but unfortunately they do not very well reflect some of the concepts of structured programming. Pseudocode, on the other hand, is a newer tool and has features that make it more reflective of the structured concepts. Unfortunately, the narrative presentation is not as easy to understand and follow.

RULES FOR PSEUDOCODE

1. Write only one stmt per line

Each stmt in your pseudocode should express just one action for the computer. If the task list is properly drawn, then in most cases each task will correspond to one line of pseudocode.

EX: TASK LIST: Read name, hourly rate, hours worked, deduction rate Perform calculations

gross = hourlyRate * hoursWorked deduction = grossPay * deductionRate net pay = grossPay deduction

Write name, gross, deduction, net pay

PSEUDOCODE: READ name, hourlyRate, hoursWorked, deductionRate grossPay = hourlyRate * hoursWorked deduction = grossPay * deductionRate netPay = grossPay deduction WRITE name, grossPay, deduction, netPay

Capitalize initial keyword

In the example above, READ and WRITE are in caps. There are just a few keywords we will use:

READ, WRITE, IF, ELSE, ENDIF, WHILE, ENDWHILE, REPEAT, UNTIL

Indent to show hierarchy

We will use a particular indentation pattern in each of the design structures:

SEQUENCE: keep statements that are stacked in sequence all starting in thesame column.

SELECTION: indent the statements that fall inside the selection structure, but not the keywords that form the selection

LOOPING: indent the statements that fall inside the loop, but not the keywords that form the loop EX: In the example above, employees whose grossPay is less than 100 do not have any deduction.

TASK LIST: Read name, hourly rate, hours worked, deduction rate Compute gross, deduction, net pay

Is gross >= 100? YES: calculate deduction

NO: no deduction Write name, gross, deduction, net pay

PSEUDOCODE: READ name, hourlyRate, hoursWorked grossPay = hourlyRate * hoursWorked IF grossPay >= 100

deduction = grossPay * deductionRate ELSE

deduction = 0 ENDIF

netPay = grossPay deduction WRITE name, grossPay, deduction, netPay

End multiline structures

See how the IF/ELSE/ENDIF is constructed above. The ENDIF (or END whatever) always is in line with the IF (or whatever starts the structure).

Keep stmts language independent

Resist the urge to write in whatever language you are most comfortable with. In the long run, you will save time! There may be special features available in the language you plan to eventually write the program in; if you are SURE it will be written in that language, then you can use the features. If not, then avoid using the special features.

SELECTION STRUCTURE

We looked at this in Chap 2:

yes

amount no< 1000

The pseudocode for this would be: IF amount < 1000

interestRate = .06 interestRate = .10

// the yes or true action // the no or false action

ELSE

interestRate = .06

ENDIF Some selections are of the do it or dont (one sided) variety. For example:

interestRate = .10

yes

average < 60?

no

The pseudocode for this is:

IF average < 60 DO SendWarning

ENDIF

DO SendWarning

It is considered poor form to have a 1-sided IF stmt where the action is on the no orELSE side. Consider this code:

IF average < 60 NULL

ELSE DO GivePassingGrade

ENDIF

This could (and should) be rewritten to eliminate the NULL yes part. To do that, wechange the < to its opposite: >= as follows:

IF average >= 60 DO GivePassingGrade

ENDIF

NESTING IF STATEMENTS

What if we wanted to put a little menu up on the screen:

Solitaire

Doom

Monopoly

and have the user select which game to play. How would we activate the correct game?

READ gameNumber IF gameNumber = 1

DO Solitaire ELSE

IF gameNumber = 2 DO Doom

ELSE DO Monopoly

ENDIF ENDIF

yes

READ gameNumber

gameNumber no= 1 ?

yes

gameNumber no=2?

DO Solitaire

DO Doom

DO Monopoly

We must pay particular attention to where the IFs end. The nested IF must be completely contained in either the IF or the ELSE part of the containing IF. Watch for and line up the matching ENDIF.

LOOPING STRUCTURES

One of the most confusing things for students first seeing a flowchart is telling the loops apart from the selections. This is because both use the diamond shape as their control symbol. In pseudocode this confusion is eliminated. To mark our loops we will use

these pairs:

START

Count = 0

The loop shown here (from the last chapter) will have the following pseudocode:

count = 0 WHILE count < 10

ADD 1 to count

WRITE count ENDWHILE

WRITE The end

WHILE / ENDWHILE

Countyes

no< 10

Notice that the connector and test at the top of the loop in the flowchart become the WHILE stmt in pseudocode. The

Add 1 to count

Write The end of the loop is marked by

end ENDWHILE.

Write count

STOP

What statement do we execute when the loop is over? The one that follows the ENDWHILE.

Sometimes it is desirable to put the steps that are inside the loop into a separate module. Then the pseudocode might be this:

Mainline count = 0 WHILE count < 10

DO Process ENDWHILE

WRITE The end

Process ADD 1 to count WRITE count

We often use this name for the first module. Initialization comes first

The processing loop uses this module Termination does clean-up

Go thru these steps and then return to the module that sent you here (Mainline)

REPEAT / UNTIL

START

Count = 0

This time we will see how to write pseudocode for an UNTIL loop:

count = 0 REPEAT

ADD 1 to count

WRITE count UNTIL count >= 10

WRITE The end

Notice how the connector at the top of the loop corresponds to the REPEAT keyword, while the test at the bottom corresponds the the UNTIL stmt. When the loop is over, control goes to the stmt following the UNTIL.

Add 1 to count

Write count

yes

WriteThe end

STOP

no >= 10

Count

ADVANTAGES AND DISADVANTAGES

Pseudocode Disadvantages

Its not visual

There is no accepted standard, so it varies widely from company to company

Pseudocode Advantages

Can be done easily on a word processor

Easily modified

Implements structured concepts well

Flowchart Disadvantages

Hard to modify

Need special software (not so much now!)

Structured design elements not all implemented

Flowchart Advantages

Standardized: all pretty much agree on the symbols and their meaning

Visual (but this does bring some limitations)

HOW WE STORE AND ACCESS DATA

What happens when we execute READ stmt? READ name, hoursWorked, hourlyRate, deductionRate

The computer stores all program data into memory locations. It knows these location by their addresses. It is perfectly able to understand code like:

READ 19087, 80976, 10943, 80764 but we would have a hard time with it. So we name our storage locations using words that are descriptive to us. Every language has its own (different) set of rules about how these names are formed. We will use a simple style:

variable names will start with a lowercase letter

they will have no spaces in them

additional words in them will start with a capital

names must be unique within the program

consistent use of names The READ statement tells the computer to get a value from the input device (keyboard,

file, ...) and store it in the names memory location.

When we need to compute a value in a program (like grossPay) we will use what is called an assignment stmt.

variable = expression

Be careful to understand the difference between these two stmts: num1 = num2

num2 = num1

The WRITE stmt is used to display information on the output device (screen, printer).To display words, enclose them in quotes. A variables value will be displayed. So if thevariable name currently contains John Smith, then the stmt

WRITE Employee name: , namewill output like this:

Employee name: John Smith

CALCULATION SYMBOLS

We will often have to represent an expression like the one that computes grossPay. To symbolize the arithmetic operators we use these symbols

grouping () exponent **or^ multiply * divide /

add + subtract -

There is a precedence or hierarchy implied in these symbols.

ORDER OF EXECUTION

() equations in parenthesis

** exponentiation

/* division and multiplication

+- addition and subtraction

Please Excuse My Dear Aunt Sally

Note: when operators of equal value are to be executed, the order of execution

is left to right.

Examples: AREA = R2

SUM = A2 + B2PERIM = 2(L + W)

A AC AC A DC D2BC B B BC B2 BC

value = 100*2/5-3 = 200/5-3 = 40-3 = 37 value = 100*2/(5-3) = 100*2/2 = 200/2 = 100 value = 100*((2/5)-3) = 100*(.4-3) = 100*-2.6 = -260

SELECTION

When we have to make a choice between actions, we almost always base that choiceon a test. The test uses phrases like is less than or is equal to. There is a universally accepted set of symbols used to represent these phrases:

> (greater than) < (less than) >= (greater than or equal to)<= (less than or = (equal to) <> (not equal to)

It is interesting to notice that these can be paired up:

SYMBOL	IS OPPOSITE TO
>	<=
<	>=
=	<>

LOGICAL OPERATORS: AND, OR, NOT AND: if any of the conditions are false, the whole expression is false.

ex: IF day = Saturday AND weather = sunny WRITE Lets go to the beach!

ENDIF OR: if any of the conditions are true, the whole expression is true

ex: IF month = June OR month = July OR month = August WRITE Yahoo! Summer vacation!

ENDIF NOT: reverses the outcome of the expression; true becomes false, false becomes true.

ex: IF day <> Saturday AND day <> Sunday WRITE Yuk, another work day

ENDIF