C_ITPR111Introduction to Programming

Learning Outcomes1.Use, develop and design structured programming methods

2. Use modularization from the chosen programming language

3. Produce appropriate documentation for a given program application.

4. Create and apply appropriate test schedules

Prescribed textbook

Pretorius C. M, Erasmus H. G, Basic Programming Principles. 2nd edition.

Pearson Education. ISBN: 9781775786030

BUT What is Programming

Programming is breaking down a task into small steps

That simple!!!!!!!!!!!!!!!

And programmers think in an unnatural way WOW!!!!

HOW

Consider this example

Put these words in alphabetic order:

apple,zebra,abacus

IF you cant manage ,then this course might soon become one of the worst experiences of your life so far…………….

So what steps were involved

Certainly you did not sit down and draw a plan of how you were going to do it because your mind does not need to.You learned to do it once when you were a child and now it just happens on its own!!!

STEPS Involved

1. You looked through the words for one beginning with “A”

2. If you found a word beginning with “A", put that word at the beginning of the list in your mind

3. Look for another word beginning with “A”

4. If there is one ,compare its second letter with the second letter of the first “A” word

5. If the second letters are different put the two words in alphabetic order using their second letters. If the second letters are the same ,proceed to the third letter and so on

6. Repeat this whole process for “B” and each letter in alphabetic order, until all the the words have moved to the appropriate place

Computers and programming Programmers have to tell the computers what to

do. Computers require these instructions to be precise

and complete in every way As humans we have an incredible brain which lets

us give vague commands and still get the correct answer. Thus, programmers have to learn to think in anunnatural way: they have to learn to take a description of a task

So tells us more about these

programmers……….. Programmers make lots of money. Programming really is fun. Programming is very intellectually rewarding. Programming makes you feel superior to other

people. Programming gives you complete control over

an innocent, vulnerable machine, which will do your evil bidding with a loyalty not even your

pet dog can rival.

Who can be a programmer?

There are a few traits which might indicate that the person would be a programmerLogicalPatientPerceptiveAt least moderately intelligentEnjoys an intellectual challenge*Gender*

What's actually involved in programming?

Write a program. Compile the program. Run the program. Debug the program. Repeat the whole process until the program is finished.

Unit 3

Programming Concepts

Programming TermsENTITY.

–An object or thing that you can describe.

• e.g a student can be described.

• A student has a name ,height ,weight , age

ATTRIBUTES

These are describing factors for an entity

Attributes describe an object or entity features

• E.g name ,height weight are the attributes of student

When completing an enrolment form about yourself, you are the entity and the information you are entering will be the attributes

Programming Terms.Variable: Variable:

A position or location in the memory of the computer where a value can be stored

It’s a variable because the value of the variable changes or varies as processing is done

Visualise it as a box in memory that contains one and only one specific value at anytime

Data type:

A data type is a classification of what kind of data the variables will hold

The attributes are the variables

An entity has attributes,characteristics

Programming TermsThe programmer must provide space for the attributes to be stored.

NB.the programmer refers to these attributes as variables

To store the attributes(variables), it should first be identified (declared)and then allocated a data type(variable type)

Examples

Description Variable Name

Name of employee empName

Price of a care carPrice

Author of a book author

Quantity in stock quantity

Age of a student stAge

Total number of sales totNumSales

Programming Terms

Data Types– Integer: Whole numbers positive or negative e.g 32, -

12, 0

– Real (float): Numbers with fractions e.g 16.35, 0.2, -987.334

– Character: A single letter, number or special character or symbols e.g “M”, “7”, “#”, “!”

– Boolean: True/false,No/Yes,0/1 e.g. Is there a lesson today?Answer Yes. Boolean value Yes/1/True

– String: two or more characters combined e.g. “Rupert”, “Error message”, “ABC” or “123”

Variable names,types and values

Description Variable name Variable type Possible value

Name of student stName String “John Smart”

Number of Books noBooks Integer 234

Price of item price Real number 78.56

Student?(y/n) student Boolean True(or 1)

Code(A-C) code Character “B”

Variable names,types and values complete the table

Description Variable name Variable type Possible value

Colour of dress

Height of a person in meters

Adult?

Age in years

Salary in R/c

Title of a book

Player in a match

Class code(K,L or M)

Name of lecturer

Number of computers

Types of variables Catagories of Variables

The number of days in a year cannot be represented as a constant nor can the number of weeks in a month. (Explain why.)

Type Description Example

Numeric variables used on numbers where calculations should take place.

Integer, Real

Non-Numeric variables

All other variables Character, String, Boolean

Constant Constantis a fixed value that cannot change throughout the entire program

Any data type e.g V.A.T in SA is 14%There are 24 hours in a dayPi is 3.14159

Arrays related variables, arrays hold numerous values but identical data types

Arrays work with index numbers and typically start at zero (0) e.g monthName[0]

Naming Variables

Naming Variables

1.The name must be unique

2.Variable name must be descriptive e.g student grade should be called grade

3.Variable name may not contain spaces but more than one word may be joined eg pages in a book could be bookPages,price of item could be item_Price

4.Variable name can contain letters and numbers eg department 234

5.A variable must start with a letter,it cannot start with a number

6.Variable name may not contain special charaters like #,&,

7.Variable name must be as short as possible while remaining descriptive.

Examples of variables:

age

department23

lastName

Naming Variables

Answer the following:

Do the following variable names comply with the rules?If not give a reason

5th grade

Member of club

Abc

5472

theAddressOfTheCompanyInTswane

grade&mark

Arrays

Defination:An array is a data structure that consists of a number of related variables.The array can hold numerous values but identical data types.An array has a single name A single variable in an array is called an element All the elements in an array are the same data type The position of an element in an array is called an index.

Arrays ExplainedWe want to have an array that stores the names of days in week.So..

The name of this array is weekDays

wekdays contains the names of the 7 days in a week

We declare the variables of this array as : day1,day2.day3,day4,day5,day6,day7

weekDays

Mon

Tue

Wed

Thur

Fri

Sat

Sun

day1

day2

day3

day4

day5

day6

day7

element index 0 element index 1

element index 2 element index3 element index 4

weekDay(0)

weekDay(1)

weekDay(2)

Weekday(3)

Arrays Explained

Day1,day2 day3 ……… are the variables.

They are of the same data type which is String

These variables have the values Mon,Tu,Wed etc

An element is then a single variable that contains a value at a given time

Index/subscript:It is the position of an element in an array.The value of an index is always positive integer or a zero

The index of the first element is always 0 and the index of the last element is (number of elements - 1) see diagram slide 24

Referencing: used to refer to a specific element.Used also to retrieve an individual value from the array.

The name of the array and the index are used.For example weekDay(0) refers to Mon,weekDay(5) refers to

Array ExampleThe names of the months of the year can be stored in a array.Each element is called month and an index is used to retrieve the individual values from the array.Fill in the missing indexes and referencies in this tableIndex Reference Value

January

February

March

April

May

June

July

August

September

October

November

December

Types of arraysOne dimensional array

Consists of one column that contains a number of row elements.

Like the example on slide 24

Two dimensional array consists of a number of rows and columns

One dimensional array two dimensional array

This array show the minimun

Temperatures for the past seven

Days of the week

345326

3 184 225 236 247 196 25This array shows the minimum and Maximum temperatures for the past Seven days.

Two dimensional array

Row zero has minimum and maximum temperatures for day 1 that is 3 and 18.

Row 3 column 0 contains minimum and maximum temperatures for day 4 that is 3 and 24

If the name of the array is temperature,to reference a particular element we specify both the row and the column number:

temperature(2,1)=23

temperature(4,0)=2

Arrays Continued

;

0 1 2 3 4 5

Step 1: Declare arrayarrBucket = new string[6];

Step 2: Place value in a bucketarrBucket[0] = “Marbles”;

Step 3: Retrieve value from bucketsystem.out.println(“The item in the first bucket

is: ” + arrBucket[0]);

The item in the first bucket is Marbles

A two-dimensional array with two rows and nine columns

An array is a data structure that consists of related data items of the same data type

Analysing and solving problem to solve a problem, we need to understand the problem. How do you make sure that you have understood the problem.

According to (Pretorius & Erasmus, 2012) Check the following:

– 1. Read the problem carefully

– 2. Understand what the problem entails

– 3. Only then write down the steps to solve the problem

Algorithm:Is a set of instruction written in a specific sequence used to solve a problem

Three phases of an algorithm:

1.What data you have available- INPUT

2. How the problem is going to be solved- PROCESSING

3. What the required results will be.- OUTPUT

Properties of an algorithm

Every algorithm has a name that describes the function or purpose of

the algorithm. The name of an algorithm starts with an uppercase letter. The last statement or step is always end. The statements or instructions between the name of the algorithm and

the end are called the body of the algorithm. A ~ (tilde) indicates that a comment, which explains the code, will

follow.A comment can be on a separate line or can follow in the same line as an instruction. A comment typically explains difficult code or why you’re including a specific instruction. A comment can be included anywhere in an algorithm.

Display means that a message or the contents of a variable are displayed (shown) on the computer screen.

Enter indicates that data must be entered via the keyboard. Calculation can also be done using equations..

Example

Determine the weekly wage of an employee when the hours he has worked and the hourly rate, are entered by the user.

Answer

CalcWage

display “How many hours did the employee work?”

enter hours

display “What is the rate of pay?”

enter rate

wage = hours * rate

display “The wage = R”, wage

end

Phases of an algorithm

An algorithm is divided into three phases:1. What data you have available to solve the problem,(INPUT)2. How you’re going to solve the problem; what steps you’re going to take, and(PROCESSING)3. What the required result is(OUTPUT)

Input is processed to produce meaningful output

Example Input processing output

Calculate the sum of two numbers and display the result on the screen:

Input: Not available in the problem statement. The user has to supply the numbers.

Processing: Add the two numbers to determine the sum.

Output: The sum as calculated in the processing phase and displayed on the computer screen.

Note the following:

• The value of the numbers must be available before the sum can be calculated.

• It is impossible to display the sum before it has been calculated

Example Input processing output

The manager of a company asks a student to do some part-time work for

which he will be paid by the hour. The student needs to know how many hours he has to work at what rate of pay before he can calculate the final amount he will receive.

INPUT/DATA: hours and the hourly rate of pay.

The input (data) must be processed to give the output (information),which is the amount the student will receive.It is clear that the input (data) is meaningless unless it is processed, becauseif the student knows how much he will receive per hour, but does not knowhow many hours he will work, the pay cannot be calculated! On the otherhand, if the student works for 20 hours but the manager hasn’t told him how

much he will earn per hour, it is also meaningless.

Input/Processing/Output (IPO) chart

Enter the name and age of a learner on the keyboard and display the name and age with a legend – which is an applicable explanation or heading to describe the output – on the computer screen

IPO chart

Input Processing Output

Name Prompt to read input fields name

age Enter input _elds age

Input/Processing/Output (IPO) chart

AlgorithmShowDetails~ This program will enter the name and the age of the learner and

display it on the screendisplay “Provide the name of the learner” ~ Display on new lineenter namedisplay “Provide the age of the learner” ~ Display on new lineenter age

~ Show the details on the screen with appropriate legendsdisplay “The name of the learner is ”, name ~ Display on new linedisplay “The age of the learner is ”, age ~ Display on new line

end

OutPut 

Provide the name of the learner John

Provide the age of the learner 18

The name of the learner is John

The age of the learner is 18

Explanation1. Words that follow the ~ sign are not executable because they’re comments

that explain what is happening or going to happen. In this case, the

purpose of the algorithm is explained.

2. The display “Provide the name of the learner” statement means that

something must be shown on the computer screen. In this case, the text

inside the quotes is displayed.

3. The enter name statement causes the computer to show a prompt on the

screen so that the user can use the keyboard to type a name. This name is

stored in the variable called name.

4. The next two statements enable the user to enter the age of a person to

store in the variable called age.

5. The display “The name of the learner is”, name statement displays the

results on the screen as follows − the words in quotes are shown exactly

as given, whereas name is a variable so its content is displayed. The

output is The name of the learner is John. We have now displayed a constant and the content of a variable. 6. The same rules apply to the next statement, which displays The age of the learner is 18.

Example 2 IPO chart

Enter the distance between two trees in kilometres. Calculate and display the distance in metres and then calculate and display the distance in centimetres

Input Processing Output

Prompt to read kilometer

Kilometer meter

Enter kilometremetre centimeter

Calculate metrecentimetre

Calculate centimetre

Display metre

Display centimetre

Example 2 algorithmConvertDistance

~ Convert km to metres and centimetres

display “Please provide the distance in km. ” ~ Display on new line

enterkilometre

~ Do the conversions

metre = kilometre * 1000

centimetre = metre * 100

~ Display the output on one line

displaykilometre, “ km is equivalent to ” , metre, “m and to ”, centimetre, “cm”

end

 

Example 3

Enter the length and the width of a tennis court in metres, then calculate

and display the perimeter and the area of the tennis court Input Processing Output length Prompt for input fields perim width Enter input fields area

Example 3 AlgorithmCalcTennisCourt

~ Calculate perimeter and area of tennis court

display “Please enter length” ~ Display on new line

enter length

display “Please enter width” ~ Display on new line

enter width

~ Do calculations and display

perim = 2 * (length + width)

area = length * width

display “The perimeter of the tennis court is ” , perim , “ metres”

display “The area of the tennis court is ” , area , “ square metres”

end

Example 3 trace tableThe input data to test this algorithm is length = 30 and width = 10

Instruction Length Width Peri Area OutputDisplay Please enter lengthenter 30Display Please enter widthEnter 10calculate perim 80calculate area 300display

The perimeter of the tennis court is 80 metre display

The area of thetennis court is 300square metres

Example 4Enter two integers on the keyboard and calculate and show the average of

these two integers on the screen.

Input Processing Output

num1 Prompt for num1 and num2 average

num2 Enter num1 and num2

Calculate average

Show average on the screen

Example4 Algorithm

CalculateAverage

~ Prompt for and enter two integers

display “Enter first number” ~ Display on new line

enter num1

display “Enter second number” ~ Display on new line

enter num2

~ Calculate average

average = (num1 + num2) / 2

~ Show average on the screen

display “The average of the two numbers is ” , average ~ Display on new line

end

Example Output

output

Enter _rst number 24

Enter second number 40

The average of the two numbers is 32

Draw the trace table for the above  

Example 5Jason works as a part-time assistant in a bookshop and receives

anhourlywage. Enter the number of hours he worked for a specific week, as well as the pay rate per hour. He has to pay R8 towards the recreation club. Calculate and display how much take-home pay he’s earned for the week.

 Input Processing Output

hours Prompt for input fields wage

rate Enter hours and rate rate

Calculate wage

Display wage on screen

Example 5

Algorithm

CalcWeeklyWage

~ Calculate and display the weekly wage for Jason

display “Provide number of hours Jason worked” ~ Display on new line

enter hours

display “Provide rate of pay” ~ Display on new line

enter rate

The input data used to test this algorithm: hours worked = 24 and rate of pay = R12.

What is the output?

Draw a trace table?

 

Example 6 HomeworkProblem Tebogo earns a monthly salary, which she divides at the

beginning of each month into amounts according to her needs. She pays R450 on rent for her room and the remainder of the money is divided as follows: 50% for food, 20% for clothes, 15% for transport, 5% for charity and the remaining amount for pocket money. Enter her monthly salary, which is never less than R1,800, on the keyboard and then calculate and display how much money she has available for the various categories.

Draw the IPO

Write the algorithm

What is the output (given that the monthly salary is R2000)

Draw the trace table

Example 7 Homework

At The Friendly Store, items can be bought individually, in which case the full amount is paid. However, customers can also buy items in bulk packages of 50 or 100, in which case a discount per item applies. There’s a 10% discount per item on bulk packages of 50, and a 12.5% discount per item on bulk packages of 100. 

Draw the IPO

Write the algorithm

What is the output (given price of one item is R50)

Complete the trace table

Instruction amtOne amt50 amt100 save1 save2 amt50 amt100 save50 save100 output

Example 8 Homework

At the EAT-A-LOT restaurant, customers dish up their own food and have th plate weighed in kg (2 decimal positions). The total weight of the plate and the food must be entered. The plate weighs 1.05 kg, which is subtracted from the total weight. The customer has to pay R7.35 per 100 g of food, and 14% VAT is added to the total. Display the weight of the food in kg as well as the amount due.

Draw the IPO

Write the algorithm

Practice exercisesIn each case, indicate the variables used, draw an IPO chart and write an algorithm to solve

the problem. Test your algorithm by doing a trace table

1,Enter two integers. Calculate and show the sum, difference and product of these two integers on the screen.

2.Enter the number of rows of chairs in the city hall as well as the number of chairs per row. Calculate and display the total number of chairs in the hall 

3.Enter Ridwaan’s height in metres and centimetres. Calculate and display his height only in centimetres (1 metre = 100 centimetres). 

4.Enter values of the minimum and maximum temperatures for a givenday, then calculate the average temperature of the day. Show the answer on the computer screen 

5.Enter any integer. Calculate double, half, a third and a quarter of the number and show the result on the screen. The data type of the result must be real. 

6.Henry rents a trailer to move stock to a store. The basic cost is R200 per day. He also pays a specific amount per kilometre travelled, entered by the owner. The owner also has to enter the kilometresand the number of days that Henry rented the trailer. Determine and show the amount due on the screen.

 

OPERATORS:

They are used to perform actions in a program. A program task is to : perform calculations make decisions based on the value of one or more variables. compare values and perform a certain action based on the outcome Operators can be divided into Arithmetic Logical.(logical gates) Relational or Comparison

Arithmetic OperatorsThese operators are used to make calculations such as addition,subtraction, multiplication and division. It tells the computer how the data should be processedOperator Description Example Answer

^ Exponentiation 2^3 8

- Negation (Not) -True False

* Multiplication 3* 4 12

/ Division 6 / 3 2

\ Integer Division 36\5 7

Mod Modulus arithmetic 37 mod 5 2

+ Addition 4 + 10 14

- Subtraction 13 – 7 6

NB:the modulas operator returns the remainder of division of two integers

Exercise Calculate the value of x in each of the following

statements:

-X = g -5 + 14 mod h ^ 2, where g = 12 and h = 1

-X = 35 mod y – (z * w + y / 3) + y * w, where w = 5, y = 24, z = 3

◊ Determine whether the expression is true or false:

m + 7 < n – 3 ^ p, where m = 4, n = 16 and p = Provide a detail solution.

Solve:

(6-2)*5+8

6*(4+7)÷22

12+14÷2-4

Logical operators Compare two expressions/variables and returns a Boolean

value.Logical expressions include AND,OR and NOT Logic operators are also called logical gates Logical gates can be combined create important

components of computers, such as the memory registers.

Operator Desciption Example Answer

AND Requires both variables/conditions to be TRUE for the result to be TRUE

True AND FalseTrue ANDTrueFalse AND False

FalseTrueFalse

OR Requires either variable/condition to be TRUE for the result to be TRUE

True OR FalseTrue OR TrueFalse OR False

TrueTrueFalse

NOT Returns TRUE if the variable/condition is FALSE and vice versa

NOT TrueNOT False

FalseTrue

Logical Operators/Logic gates

Logical Operators/Logic gates

A B A.BFalse False FalseFalse True FalseTrue False FalseTrue True True

A B A+BFalse False FalseFalse True FalseTrue False FalseTrue True True

A ĀFalse TrueTrue False

Logical Operators/Logic gates Switching circuits that perform certain simple operations

on binary signals Have one or two inputs Have one output Inputs and output is one bit in size with a value of either 0

(false) or 1 (true) Basic building blocks of computers and all other digital

devices Can be combined to perform useful and more complex

functions.

ExerciseEvaluate the following expressions:D OR K AND NOT S; where D = TRUE, K = FALSE, S = TRUEM > 7 AND D < S ^ 2; where M = 7, D = 8, S = 4NOT F OR E AND D + C = A; where A = 5, C = 12, D = -4, E = TRUE and F = FALSE

Relational operators Comparison operators compare two numeric or two

character values. A numeric value cannot be compared with a character value.

Operator Description Example = Equal to A = 10 > Greater than number > 50 < Smaller than total < 21 <> Not equal to age <> 0 >= Greater &equal to Weight <>35 <= Smaller & equal to SubjectCount <=6

Exercise

Evaluate the following expressions:

A + T <> (A + B) * 4; where A = 4, B = 17 and T = 20

“true” = 30

Program flowcharts The program flowchart (design)illustrates the logic of the

program and gives details on manipulating the data Just as a builder cannot build a house without a properly

drawn plan ,one should never code a program without a proper design(flowchart)

Program flowcharts are constructed with a set of standardised

symbols that make it easier for persons other than the original programmer to read and maintain the program.

For each symbol in flow chart there is corresponding pseudo code statement

Flowcharts A graphical representation of the sequence of

operations in an information system or program.

Program flowcharts show the sequence of instructions in a single program or subroutine.

– shows logic of an algorithm– emphasizes individual steps and their

interconnections– e.g. control flow from one action to the next

Note: Different symbols are used to draw each type of flowchart.

Flowchart SymbolsSymbol Example and Function

TerminatorIndicates the beginning, end or interruption of a program

Process

Represents program instructions that process data

Decision

Y

N Indication branching based on a decision is made

start

stop

gPay=rate*hours

stopEOF

Flowchart SymbolsSymbol Example and Function

For loop Loops through statements

ConnectorRepresents a connection in flow

Off-page connectorUsed instead of the connector when the flow continues to the next page

AB

More Flowchart SymbolsProcess Symbol Pseudocode

Initialisatiom totHours=0

Assignment totHours=totHours+hours

Input statementInput name,hours

Read statement Read name,hours

Output statement Print “my name is Java”

tot Hours=0

totHours=totHours+hours

Input name,hours

Read name,hours

Print”my name is Java”

pseudocode?

What is pseudocode?Structured English (formalized and abbreviated to look like high-level computer language)

Example 1:

Write an Pseudocode to determine a student’s final grade and indicate whether it is passing or failing. The final grade is calculated as the average of four marks.

Example 1-Pseudocode

Pseudocode: Input a set of 4 marks Calculate their average by summing and dividing

by 4 if average is below 50

Print “FAIL”else

Print “PASS”

Example 2

Write an pseudocode and draw a flowchart to convert the length in metres to centimeter.

Pseudocode: Input the length in metre (m) Calculate the length in cm (Lcm) by

multiplying m with 100 Print length in cm (LCM)

START

Inputm

Lcm m x 100

PrintLcm

STOP

Print Lcm

Example 3

Write pseudocode and draw a flowchart that will read the two sides of a rectangle and calculate its area.

Pseudocode Input the width (W) and Length (L) of a rectangle Calculate the area (A) by multiplying L with W Print A

Example 3 Flow chart

START

InputW, L

A L x W

PrintA

STOP

Print A

Example 4 Write pseudocode and draw a flowchart that will

calculate the roots of a quadratic equation

Hint: d = sqrt ( ), and the roots are: x1 = (–b + d)/2a and x2 = (–b – d)/2a

Pseudocode: Input the coefficients (a, b, c) of the quadratic equation

Calculate d

Calculate x1

Calculate x2

Print x1 and x2

Example 4 FlowchartSTART

Inputa, b, c

d = sqrt(b x b – 4 x a x c)

Printx1 ,x2

STOP

x1 =(–b + d) / (2 x a)

X2 = (–b – d) / (2 x a)

Decision Structures The expression A>B is a logical expression it describes a condition we want to test if A>B is true (if A is greater than B) we take the

action on left print the value of A if A>B is false (if A is not greater than B) we take

the action on right print the value of B

Decision Structures

isA>B

Print BPrint A

Y N

Print A Print B

IF–THEN–ELSE STRUCTURE

The structure is as follows

If condition then

true alternative

else

false alternative

End if

IF–THEN–ELSE STRUCTURE

The pseudocode for the flowchart is as follows:

If A>B then print A

else print B

endif

Example 5 Write an pseudocode that reads two values, determines the

largest value and prints the largest value with an identifying message.

Pseudocode Input VALUE1, VALUE2

if (VALUE1 > VALUE2) then MAX = VALUE1

else MAX=VALUE2

endifPrint “The largest value is”, MAX

Example 5 Flowchart

MAX =VALUE11

Print“The largest value is”, MAX

STOP

Y N

START

InputVALUE1,VALUE2

MAX = VALUE2

isVALUE1>VALUE2

Print“The largest value is”, MAX

Naming Variables The name must be unique The name must be descriptive The name may not contain spaces A name can contain letters and numbers but NOT NUMBERS

ONLY A variable name must start with a letter A variable name may not contain special characters A variable name should be as short as possible Description Name

Name of employee empName

Price of car carPrice

Author of book Author

Quantity in stock Quantity

Age of student stAge

Total number of sales totNumSales

Do the following variable names comply with the rules? If not, give a reason

5thGrademember of club abc5472 theAddressOfTheCompanyInTshwanegrade&mark

Complete the table

Complete the table-naming variablesDescription Variable name Variable type Possible value

Colour of dress

Height of person in metres

Adult?

Age in years

Salary in R/c

Class code (K, L or M)

Number of computers

Name of lecturer

Functions A function is a group of statements that perform a specific

task and returns a value to the part of the programm that called it

The value that is returned can

– Be assigned to a variable

– Displayed on the screen

– Used in a mathematical expression When you want to execute it you call it. NB:instead of having an equation in the main program a

function can be used

Structure of a functionFunction FunctionName(parameterList)

Statements

Statements

Etc

Return value

End function

Example Function to add two numbers

Function sum(num1,num2)

Result=num1+ num2

Return result

End Function

FunctionsA function can be called as part of the calculation in the main program

Example

total= Function sum(firstNumber,secondNumber) + 200

A fucntion can be called as a variable that will store the value of the answer

Example

studTotal=Function sum(firstNumber,secondNumber)

Worked out examplean assignment statement

Write a calling statement to call a function that calculates the sum of two numbers as well as the function to store the answer in a variable called sum.

Calling Statement

Sum= CalcSum(number1,number2)

The function to calculate 2 numbers

Function calcSum(valNumber1,valNumber2)

total = valNumber1,+ valNumber2)

return total

End function

What is happening in the example

Main program

Sum = Function calcSum(number1,number2)

calcSum(valNumber1,valNumber1)Total = valNumber1 + valNumber2

Return total

End function

function

What is happenning in the examplenumber1 and number2 are the arguments(value

parameters)In the main program the answer will be stored in sum valNumber1 and valNumber2 are the parameter list.Function and main program communicate by

parametersOrder the order of the parameters must be the same as

in the functions

Worked out Display statement

Supposs we do not want to store the answer in sum but we want to display the sum of the two numbers,the calling statement would be :

Display”the sum is”,calcSum(number1,number2)

Worked out wxampleif statement

The function can be called and the sum is used in the if statement

If calcSum(number1,number2) > 40 then

Display “the sum is greater than 40”

endif

A complete pseudocode using a functionThe program displays the total age for two friends

~get the user’s age and the user’s best friend ageSumOfTwoAges

Display”enter your age”

Input firstAge

Display”enter your friend’s age”

Input secondAge

~get the sum of both

total = sum (firstAge , secondAge )

~display the sum

Display” Together you are “total “years old”

End

~the sum function accepts two integer arguments and returns the sum of those arguments

Function sum(num1,num2)

Result= num1 + num2

Return result

End Function

What is happenning in the above programIn the main program the program gets two values from the user and stores these in the firstAge and secondAge variables. The statement :total = sum (firstAge , secondAge )

calls the sum function passing firstAge and secondAge as arguments.The value that is returned from the sum function is assigned to total variable .

NB:A function parameter list can be empty see following example

An empty parameter listWrite a program that computes the sale price fpr an item in a retail business.

To do that you will need to get the regular price of the item from the user.The function to do that would be:

Function getRegularPrice()

~get regular price

Display”enter the item’s regular price”

Input price

~return the regular price

Return price

End Function

In the main program to call that function :~get the item’s regular price

regularPrice = getRegularPrice()

Program with two functionThe program calcu;ates the sale price for an itemconstant DISCOUNT_PERCENTAGE

~The main program is the starting point of the program

SalePrice

~get item’s regular price

regularPrice = getRegularPrice()

~calculate sale price

salePrice=regularPrice-discount (regularPrice)

~Display Sale price

Display “The sale price is “ salePrice

End

~The getRegularPrice fmction prompts user to enter regular price of item and returns the price

Function getRegularPrice()

~get the regular price

Display ” Enter the item’s regular price

Input price

Return price

End

~The discount function accepts an item’s price as an argument and returns the amount of discount Function discount(price)

Return price * DISCOUNT_PERCENTAGE

End Function

About Functions The function name used in the calling statement and the function name

in the function header must always be the same. The names of the arguments and parameters need not be the same. The order of the variables in a calling statement’s argument list and the

parameters in the function header must always be the same. The number of variables in a calling statement’s argument list and the

number of parameters in the function header must always be the same. The name of the value returned by the function need not be the same as

in the calling statement. The arguments are only the names of the applicable variables in the

calling module. On the other hand, the parameters in the header must

indicate whether the parameter is a value parameter or a reference parameter – in other words, whether a copy or an address has been sent

Parameter A parameter is data (variables or values)

that is sent to a function, which it (function) needs to perform the task it has to do

Two types of parameters value parameters

– only a copy of the argument’s value is passed to the parameter variable

– If the contents of the parameter variable change it has no effect on the argument on the calling program

reference parameters.– Allows the module to change/modify the argument in the calling

part of the program

Variable scope is the part of the program in which the variable may be accessed

Argument ,ParameterArgument

any piece of data that is passed to the function when that function is called

Parameter

a variable that receives an argument that is passed into the function

Example 1(Functions)Reginald went to a shop to buy a number of fruit bars. The number bought

and the price of a fruit bar are entered in a main procedure. These numbers

need to be sent to a function to calculate the amount due. The amount due

must include 14% VAT. The calculated value must be returned to the main

procedure and displayed on the screen

PLANNING

Input and Output for the function and the main program

Description Type Variable nameMain procedure (ShoppingProgram)Input Number of items Integer numItems Price of one item Real priceOutput Amount due Real amtDueFunction (CalcAmtDue)Input Copy of number of items Integer valNum

Copy of price of one item Real valPrice

Output Amount due Real -not used-

Algorithm for Example 1Function CalcAmtDue (valNum, valPrice)

return (valNum * valPrice * 1.14)

ShoppingProgram

~ The input data will be entered in the main procedure.

~ The main procedure will call a function to calculate the amount due.

~ The amount due will be displayed in the main procedure.

display “Enter the number of fruit bars bought”

enter numItems

display “Enter the price of a fruit bar”

enter price

amtDue = CalcAmtDue (numItems, price) ~ Function call

display “The amount due is R”, amtDue

end

Example 2 functionsWrite an algorithm to enter three test marks for a student. A function is called to calculate the average mark. Another function is used to indicate whether the average mark is a pass mark (>=50) or a fail mark. The average as well as the result must be displayed on the screen. All input and output must be done in the main procedurePlanning

Description Type Variable name

Main procedure (ShowResults)

Input Student name String studentName

Test mark 1 Integer testMark1

Test mark 2 Integer testMark2

Test mark 3 Integer testMark3

Output Average mark Real average

Result String -not used-

Function (CalcAve)

Input Copy of test mark1 Integer valTest1

Copy of test mark2 Integer valTest2

Copy of test mark3 Integer valTest3

Output Average mark Real -not used-

Function (DetermineResults)

Input Copy of averagemark integer valAve

Output Result message String message

Algorithm for example2Function CalcAve (valTest1, valTest2, valTest3) ~ Function

~ Calculate and return the average of the three tests

return (valTest1 + valTest2 + valTest3) / 3

Function DetermineResults (valAve) ~ Function

~ Produce a message to express the outcome

message = “pass”

if valAve < 50 then

message = “fail”

endif

return message

ShowResults ~ Main procedure

~ This program determines the result of the student’s performance

display “Enter the student name”

enter studentName

display “Enter the first test mark”

enter testMark1

display “Enter the second test mark”

enter testMark2

display “Enter the third test mark”

enter testMark3

~ Call the function to calculate the average

average = CalcAve (testMark1, testMark2, testMark3)

display “The average mark for ”, studentName , “ is ”, average

~ Call the function to determine the result

display “This student will ”, DetermineResults(average)

end

Example3Identify and correct all the errors in the following function call and its

corresponding function header.

decPay = CalcPay(Hours, Tariff )

Function Pay(refTariff, valHours)

Answer

1.The function name should be the same in the function and in the statement calling the function i.e CalcPay should be Pay

2.The order of the parameters should be the same in the function and in the calling ststement i.e decPay = CalcPay(Tarrif, Hours )

Function Pay(refTariff, valHours)

Example 4Determine the output of each of the following algorithms:

Function Calculation(valX, valY)

return (valX + valY \ 2)

JustACalculation

a = 14

b = 5

answer = Calculation(a, b)

display “The answer is ”, answer

End

Answer

Output

The answer is 9

Example 5What is the output ?

Function AddNumbers(valA, valB)

c= valA + valB

return c

MainAlgorithm

a = 0

b = 1

do while a < 5

x = AddNumbers(a, b)

b = a + 5

a = a + 1

display “a = ”, a , “ b = ”, b , “ x = ”, x ~ Display on a new line

loop

End

Answer

OUTPUT

a = 1,b = 5, X = 1

a = 2, b = 6, X = 6

a = 3, b = 7 , X = 8

a = 4 , b = 8 , X = 10

TRY THE FOLLOWING ON YOUR OWN!1. Study each of the following function calls, then write the complete

function to calculate and return the answer.

1.1 BestMark = DetermineBest(Test1, Test2, Test3)

The function must determine and return the best of the three test

marks.

1.2 Average = CalcAverage(Test1,Test2, Test3)

The function must calculate and return the average of the three test

marks.

1.3Pay = CalcPay(Hours, Tariff )

The function must calculate the person’s pay by multiplying the hours

by the tariff per hour. If there are more than 40 hours, the person

receives 1½ times the tariff for all hours over 40.

1.4 NetMonthSal = CalcSal(GrossAnnSal, TaxPercentage)

The function must calculate and return an employee’s net monthly

salary from their annual gross salary as well as the percentage tax that

the person must pay. Deduct the tax amount from the monthly gross

salary to calculate the monthly net salary.

TRY THE FOLLOWING ON YOUR OWN!

Write a complete algorithm with functions to solve the following problem:

Enter the radius of a circle, then call one function to calculate the

circumference and another function to calculate the area of the circle.

Display the calculated values on the screen.

ALL THE BEST !!!

Subprocedures It can receive value parameters to use in the subprocedure It can receive reference parameters. It doesn’t return a value. It is able to manipulate data outside the subprocedure at specific addresses, as given in the reference parameters. In other words, it can change more than one value.

The subprocedure call syntax

call NameOfSubProcedure (argument list)

Example:

call Calculations(number1, number2, sum, product)

display “The sum of ”, number1, “ and ”, number2, “ = ”, sum

display “The product of ”, number1, “ and ”, number2, “ = ”, product

Calculations is the name of the subprocedure

number1 and number2 are value parameters they will not change

sum and product are two reference parameters values in these specific addresses may be changed

Subprocedure call

Subprocedures

call Calculations(number1, number2, sum, product)

The above is a subprocedure call.The actual subprocedure would be

Sub Calculations(valNo1, valNo2, refSum, refProduct)

~ Calculate the sum and the product of 2 numbers

refSum = valNo1 + valNo2

refProduct = valNo1 * valNo2

End Sub

NB: A function or subprocedure can be called from a main procedure or from

any other function or subprocedure as can be seen in some of the examples

Worked Example Subprocedure 1

Danny invested an amount at the Save-a-Lot Bank, which must be entered at

the beginning of the algorithm. The monthly interest rate is also entered. The

algorithm must calculate and display the amount of interest earned as well as

the balance at the end of every month for the next 15 months. At the end of

the algorithm the total amount of interest must be displayed. This example

uses functions and subprocedures where possible. A monthly interest rate is

used to test the program, for example an annual interest rate of 10% = 0.83%

per month.

Worked Example Subprocedure 1Algorithm

Sub DisplayResults (valMonth, valAmt, valMInt) ~ Display monthly values

display valMonth, “ ”, valAmt, “ ” , valMInt

End Sub

Sub CalcNewValues (valRate, refAmt, refMonthInterest)

refMonthInterest = refAmt * valRate / 100 ~ Calculate interest

refAmt = refAmt + refMonthInterest ~ increase amount

End Sub

Sub AccSum (valMInterest, refTInterest)

refTInterest = refTInterest + valMInterest ~ Accumulate interest total

End Sub

EarnInterest

~ This program deals with the investment of money

totInterest = 0

monInt = 0

~display Headings

display “Provide the amount you want to invest”

enter amount

display “Enter the monthly interest rate”

enter rate

call DisplayResults (0, amount, monInt) ~ Display initial values

~ Repeat 15 times to obtain final results

for x = 1 to 15

call CalcNewValues (rate, amount, monInt)

call DisplayResults (x, amount, monInt)

call AccSum (monInt, totInterest)

next x

display “The total amount of interest earned is R”, totInterest

end

Worked Example Subprocedure 2Write an algorithm to calculate the final marks students obtained for Programming 3. The final mark is calculated on the marks of various assessments and their particular weightings:

Assessment Weighting

Test 1 15%

Test 2 20%

The better of two classtest marks 15%

Examination 50%

HINT:

We’ll code a function to determine and return the higher mark of two class

tests. A subprocedure will be used to calculate the final mark and determine

whether it is a pass or fail (message), and another subprocedure will display the

mark and the message result.

AnswerFunction CalcClMark (valClMark1, valClMark2) ~ Function header

if valClMark1 > valClMark2

betterMark = valClMark1

else

betterMark = valClMark2

endif

return betterMark

Worked Example Subprocedure 2Sub CalcValues (valTest1, valTest2,valClassTest,valExam) ~ Subprocedure

final = valTest1 * 0.15 + valTest2 * 0.2 + valClassTest * 0.15 + valExam * 0.5

if final >= 50 then

message = “Pass”

else

message = “fail”

endif

call DisplayResults (final, message)

End Sub

Sub DisplayResults (valFinalMark, valMessage) ~ Subprocedure

display “The final mark of the student is “, valFinalMark

display “The result is “, valMessage

End Sub

CalcFinalMark

Main procedure

display “Provide the mark for test 1”

enter test1

display “Provide the mark for test 2”

enter test2

display “Provide the mark for class test 1”

enter clTest1

display “Provide the mark for class test 2”

enter clTest2

display “Provide the exam mark”

enter exam

betterClassTest = CalcClMark (clTest1, clTest2) ~ Function call

call CalcValues (test1, test2, betterClassTest, Exam) ~ Call subprocedure

end

As mentioned earlier, a function or subprocedure can be called from a

main procedure or from any other function or subprocedure.

Determine the outputSub IsntItLovely (valA, refB, valC, refD)

refD = valA

if refB mod 3 = 0 then

refB = refB + 2

endif

refD = valA + (valC mod 5)

valA = valA + 2

valC = valC + 1

End Sub

MainAlgorithm

w = 0

x = 3

y = 8

z = 6

for m = 4 to 9 step 3

w = m

call IsntItLovely(w,x,y,z)

display “w = ” , w , “ x = ” , x , “ y = ” , y , “z = ”, z

next m

end

Determine the outputSub CalcProc (valA, refB)

c = valA * 3

refB = c - refB

End Sub

Function CalcFunc (valK)

return ((valK * 2) mod 4)

MainModule

m = 4

l = 1

k = 2

do

j = CalcFunc (m)

call CalcProc (j, k)

display “ l = “ , l , “ j = “ , j , “k = “, k , “m = “, m

m = m + 1

loop until m > 5

end