6 Function

CSWD1001
Programming Methods
Function
18/9/2018
CSWD1001 @ Kwan Lee First City Unversity Malaysia
(FCUC)
1

What we’ll learn
• Introduction to functions
• Writing your own functions
• More library functions
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What is Function
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Definition
• A functions is a module that returns a value back to the part
of the program that called it
• Most programming languages provide a library of prewritten
functions that perform commonly needed tasks.
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Remember Function
is
Different
from Module
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• Functions are called differently than modules
• In pseudocode, you use the Call statement to call a module.
You do not use the Call statement to call a function.
• Function calls are
• usually inserted into statements that perform some operation with
the value that is returned from the function.
• might also be inserted into a Display statement that displays the
value that is returned from the function.
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Library Function
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Characteristic of Library Function
• Library function:
• Are built into the programming language, and you can call them any time you
need them
• Usually stored in special files
• When you call a library function in one of your programs, the
compiler or interpreter automatically causes the function to execute,
without requiring the function’s code to appear in your program.
• You never have to see the code for a library function – you only need
to know the purpose of the library function, the arguments that you
must pass to it, and what type of data it returns.
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Example – Random function
• Commonly used in games, example computer games that let the player
roll dice use random numbers to represent the values of the dice
• Useful in simulation programs. Formulas can be constructed in which
a random number is used to determine various actions and events that
take place in the program
• Useful in statistical programs that must randomly select data for
analysis
• Commonly used in computer security to encrypt sensitive data
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Pseudocode
// Declare a variable to control the loop iterations.
Declare String again
Do
// Roll the dice.
Display "Rolling the dice..."
Display "Their values are:"
Display random(1, 6)
Display random(1, 6)
// Do this again?
Display "Want to roll them again? (y = yes)"
Input again
While again == "y" OR again == "Y"
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Flowchart
Start
Declare String again
Display “Rolling the dice…”
Display “Their values are.”
Display random(1,6)
Display random(1,6)
Display “Want to roll tem again?
(y = yes)”
Input again
again ==
“y” OR
again ==
“Y”
End
True
False
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More library function – mathematical
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More library function – data type conversion
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More library function – string function
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You can Write your Own Function
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Characteristic of Own Function
• Most programming languages allow you to write your own
functions.
• When you write a function, you are essentially writing a
module that can send a value back to the part of the program
that called it
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Declaration of Function
Function DataType FunctionName(ParameterList)
Statement
Statement
Statement
Etc
Return value
End Fuction
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Example Use Case Writing own Function
• Hal owns a business named Make Your Own Music, which sells
guitars, drums, banjos, synthesizers, and many other musical
instruments.
• Hal’s sales staff works strictly on commission. At the end of the
month, each salesperson’s commission is calculated according to table
below:
Sales This Month Commission Rate
Less than $10, 000.00 10%
$10,000.00 – 14, 999.99 12%
$15,000.00 – 17, 999.99 14%
$18,000.00 – 21, 999.99 16%
$22,000.00 or more 18%
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• For example, a salesperson with $16,000 in monthly sales will earn a
14 percent commission ($2,240). Another salesperson with $20,000 in
monthly sales will earn a 16 percent commission ($3,200). A person
with $30,000 in sales will earn an 18 percent commission ($5,400).
• Because the staff gets paid once per month, Hal allows each employee
to take up to $2,000 per month in advance. When sales commissions
are calculated, the amount of each employee’s advanced pay is
subtracted from the commission.
• If any salesperson’s commission is less than the amount of his or her
advance, the salesperson must reimburse Hal for the difference.
• To calculate a salesperson’s monthly pay, Hal uses the following
formula:
Pay = Sales × Commission rate – Advanced pay
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• Hal has asked you to write a program that makes this calculation for
him. The following general algorithm outlines the steps the program
must take:
1. Get the salesperson’s monthly sales.
2. Get the amount of advanced pay.
3. Use the amount of monthly sales to determine the commission rate.
4. Calculate the salesperson’s pay using the formula previously shown. If the
amount is negative, indicate that the salesperson must reimburse the
company.
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Pseudocode Commission Rate Program:
Main Module
Module main()
// Local variables
Declare Real sales, commissionRate, advancedPay
// Get the amount of sales.
Set sales = getSales()
// Get the amount of advanced pay.
Set advancedPay = getAdvancedPay()
// Determine the commission rate.
Set commissionRate = determineCommissionRate(sales)
// Calculate the pay.
Set pay = sales * commissionRate - advancedPay
// Display the amount of pay.
Display "The pay is $", pay
// Determine whether the pay is negative.
If pay < 0 Then
Display "The salesperson must reimburse the
company."
End If
End Module
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getSales Function
// The getSales function gets a salesperson's monthly sales from the user and returns
// that value as a Real.
Function Real getSales()
// Local variable to hold the monthly sales.
Declare Real monthlySales
// Get the amount of monthly sales.
Display "Enter the salesperson's monthly sales."
Input monthlySales
// Return the amount of monthly sales.
Return monthlySales
End Function
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getadvancedpay Function
// The getAdvancedPay function gets the amount of // advanced pay given to the salesperson and
// returns that amount as a Real.
Function Real getAdvancedPay()
// Local variable to hold the advanced pay.
Declare Real advanced
// Get the amount of advanced pay.
Display "Enter the amount of advanced pay, or 0 if no advanced pay was given."
Input advanced
// Return the advanced pay.
Return advanced
End Function
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determineCommissionRate Function
//The determineCommissionRate function accepts the
// amount of sales as an argument and returns the
// commission rate as a Real.
Function Real determineCommissionRate(Real sales)
// Local variable to hold commission rate.
Declare Real rate
// Determine the commission rate.
If sales < 10000.00 Then
Set rate = 0.10
Else If sales >= 10000.00 AND sales <= 14999.99 Then
Set rate = 0.12
Set rate = 0.14
Set rate = 0.16
Else
Set rate = 0.18
End If
// Return the commission rate.
Return rate
End Function
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Flowchart
Main Module
Main()
Declare Real sales,
commissionRate, advancedPay
Set sales = getSales()
Set advancedPay =
getAdvancedPay()
Set commissionRate =
determineCommissionRate(sales)
Set pay = sales *
commissionRate - advancedPay
Display “The pay
is $”, pay
pay < 0
End
Display “The
salesperson must
reimburse the
company ”
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Flowchart
getSales
Function
getSales()
Declare Real monthlySales
Display “Enter the
sales-person’s
monthly sa;es”
Input monthlySales
Return
monthlySales
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Flowchart
getadvancedpay
Function
getAdvancedpay()
Declare Real adanced
Display “Enter the
amount of advanced
pay, or 0 if no advanced
pay was given”
Input advanced
Return
advanced
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Flowchart
determineComm
issionRate
Function
determineCom
missionRate(Re
al sales)
Declare Real rate
Sales <
10000.00
Set rate = 0.10
Sales >=
10000.00
AND sales
<=
14999.99
Sales >=
15000.00
AND sales
<=
17999.99
Sales >=
18000.00
AND sales
<=
21999.99
Set rate = 0.12
Set rate = 0.14
Set rate = 0.16Set rate = 0.18
Return rate
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Using IPO Charts
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Definition
• IPO stands for input, processing, and output, and an IPO chart
describes the input, processing, and output of a function.
• Simple but effective tool that programmers sometimes use while
designing functions
• These items are usually laid out in columns:
• the input column - description of the data that is passed to the function as
arguments;
• the processing column - description of the process that the function
performs;and
• the output column - describes the data that is returned from the function.
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IPO charts for the getRegularPrice and
discount functions
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Pseudocode
// Global constant for the discount percentage.
Constant Real DISCOUNT_PERCENTAGE = 0.20
// The main module is the program's starting point.
Module main()
// Local variables to hold regular and sale
prices.
Declare Real regularPrice, salePrice
// Get the item's regular price.
Set regularPrice = getRegularPrice()
// Calculate the sale price.
Set salePrice = regularPrice -
discount(regularPrice)
// Display the sale price.
Display "The sale price is $", salePrice
End Module
// The getRegularPrice function prompts the user to
// enter an item's regular price and returns that
// value as a Real.
Function Real getRegularPrice()
// Local variable to hold the price.
Declare Real price
// Get the regular price.
Display "Enter the item's regular price."
Input price
// Return the regular price.
Return price
End Function
// The discount function accepts an item's price
// as an argument and returns the amount of the
// discount specified by DISCOUNT_PERCENTAGE.
Function Real discount(Real price)
Return price * DISCOUNT_PERCENTAGE
End Function
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Function allow
a Return
as
Strings / Boolean
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Functions That Return Strings
Function String getName()
//Local variable to hold the user’s name
Declare String name
//Get the user’s name
Display “Enter your name”
Input name
//Return the name
Return name
End Function
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Functions That Return Either True Or False
Function Boolean isEvent(Integer number)
//Local variable to hold True or False
Declare Boolean status
//Determine whether number is even. If it is, set status to
true. Otherwise, set status to false.
If number MOD 2 == 0 Then
Set status = True
Else
Set status = False
// Return the value in the status variable
Return status
End Function
If isEven(number) Then
Display “The number is even”
Else
Display “The number is odd”
End If
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Summary
• A function is a module that returns a value back to the part of the
program that called it. Most programming languages provide a library
of prewritten functions that perform commonly needed tasks. In these
libraries you typically find a function that generates random numbers.
• Most programming languages allow you to write your own functions.
When you write a function, you are essentially writing a module that
can send a value back to the part of the program that called it.
• An IPO chart is a simple but effective tool that programmers
sometimes use while designing functions
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37

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