Transcript Intro to the AS/400 - Florida State College at Jacksonville

Intro to Programming
& Algorithm Design
Functions
Assg
This presentation can be viewed on line in a file named:
ch06.IntrotoProg.Functions.ppt
Copyright 2003 by Janson Industries
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Objectives
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Explain
■
What a function is
■
How to use and create
functions
■
IPO Charts
Show how to implement and
use functions in Java
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Function
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▀
Per text: “Functions are methods/
modules that return a value”
Just as with methods, the function
header defines the function's
■
■
▀
The function header also defines
■
▀
Name
Expected values (arguments)
The returned value type (Real, String)
And the body must contain
■
A Return statement
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Function
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In pseudocode, function starts
with the word Function and ends
with End Function
Function String captureInput()
Declare String data
Display “Enter input”
Input data
Return data
End Function
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Function
▀
▀
A function's returned value can be
assigned to a variable
Call a function just like a module:
■
Specify the function name
followed by parenthesis
Module main()
Declare String subtotal
subtotal = captureInput()
End Module
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Does captureInput accept any
data?
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All Pseudocode
Module main()
Declare String subtotal
subtotal = captureInput()
End Module
Function String captureInput()
Declare String data
Display “Enter input”
Input data
Return data
End Function
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6
Function Calls Flowchart
captureInput()
main()
Declare String
subtotal
Declare String
data
Display “Enter input”
subtotal =
captureInput()
Input data
End
Return data
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SFC
Specify Function
The return value type
The variable/value to return
Function name
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SFC
Then add function
statements
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SFC
Finished function
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Raptor
▀
Doesn't support
functions
Finished function
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Raptor
When run
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Java
▀
Java very similar to pseudocode
The return value type
Function name
The value/variable to return
▀
What will be the result?
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Prewritten Functions
▀
▀
Supplied with programming
language
Example: System.out.println() the
println function is invoked in a
class called System
■
▀
You can tell because () follows
the name
This is an example of a function
that will accept a parameter
■
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System.out.println("Stuff");
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Why Create Functions
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▀
▀
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Just as with methods, cuts down
on duplicate code
Make it easier for programmer
For instance, System.out.println()
is a lot to type
Will create a class called MyUtils
■
Create a function called p(String output)
■
Will be able to specify MyUtils.p()
instead of System.out.println()
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Pre-Written functions
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MyUtils just acts as a repository of
useful functions
■
So, no need for a main()
public class MyUtils {
}
public static int p(String output){
System.out.println(output);
return 1;
}
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Pre-Written Functions
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Now any other class can use the
function p()
In any java class, just specify
■
ClassName.functionName();
public class FunctionCall2 {
}
public static void main(String[] args) {
MyUtils.p(“Howdy”);
}
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When FunctionCall2 is run, it invokes p in MyUtils
Must compile MyUtils before FunctionCall2
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Prewritten Functions
▀
Most languages come with many
to perform common functions
■
Mathematical functions
♦
■
Generate a random number
■
Convert between data types
■
Displaying (println)
■
Exiting
■
Security
♦
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Sine, cosine, square root, etc.
Userid/PW, cryptography
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Prewritten Functions
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Advantage of prewritten functions
■
Don't have to create the function
yourself
■
Don't have to understand how it
works
♦
■
Called implementation hiding
You're sure they work
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Prewritten Functions
▀
Some examples
■
random(#,#) – returns a number
between the first (inclusive) and
second number (inclusive)
♦
■
pow(#,#) – raises the first number to
the power of the second number
♦
■
pow(2,4) returns 16
round(#.#) – returns an integer
value for a real value
♦
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random(1,6) returns a number
between 1 and 6
♦
round(3.49) returns 3
round(3.5) returns 4
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Prewritten Functions
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Some examples
■
isInteger(string) – returns a Boolean
value based on whether the string
can be converted to an integer
♦
■
isInteger("6") returns a value of true
isReal(string) – returns a Boolean
value based on whether the string
can be converted to a Real
♦
isReal(“abc”) returns a value of false
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Prewritten Functions
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Converting data types
All data entered is String must
convert to get numeric value
■
stringToInteger(string) – returns the
integer value of the string
♦
■
stringToInteger(“6”) returns the number 6
stringToReal(string)– returns the real
value of the string
♦
stringToReal(“2.14”) returns the number
2.14
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Prewritten Functions
▀
String functions
■
length(string) – returns the number of
characters in a string
♦
■
substring(string, 3, 5)– returns the
characters from position 3 to 5
♦
■
substring(“goodbye”, 3, 5) returns the
string “db”
contains(string, string)– returns
Boolean value of true or false based
on if the first string contains the
characters in the second string
♦
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length(“hello”) returns the number 5
contains(“goodbye”, “oo”) returns the
value true
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Prewritten Functions Example
▀
Will enhance the captureInput
function to convert the data into a
numeric value
Module main()
Declare Real subtotal
Display “Enter number”
subtotal = captureInput()
End Module
25
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Prewritten Functions Example
Function Real captureInput()
Declare String data
Declare Real numberInput
Display “Enter a number”
Input data
While(!(isReal(data)))
Display “Please enter a number”
Input data
EndWhile
numberInput = stringToReal(data)
Return numberInput
End Function
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Prewritten
Functions
Example
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Prewritten Functions Java
▀
Are in classes like Math, Integer,
Double, String
■
Math.pow(#,#) – raises the first
number to the power of the second
number
♦
■
Math.pow(2,4) returns 16
Math.round(#.#) – returns an integer
value for a real value
♦
♦
Math.round(3.49) returns 3
Math.round(3.5) returns 4
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Prewritten Functions Java
▀
Some examples
■
Math.random() – returns a number
between 0 and 1(exclusive)
♦
To get an int in a range, must multiply
the result by the max value & add one,
then change to an int (truncate)
• (int) (Math.random()*6) +1
■
Random class has nextInt(#) method
that returns a number from a range
0(inclusive) to #(exclusive)
♦
Random.nextInt(7)
• Returns integer value of 0, 1, 2, 3, 4, 5, or 6
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Prewritten Functions Java
▀
▀
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Converting data types
All data entered is String must
convert to get numeric value
■
Integer.valueOf("6")
■
Double.valueOf("2.14")
There are no isReal or isInteger
functions in java
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Prewritten Functions Java
▀
String functions
■
Assuming:
♦
String testString = new String("Goodbye");
■
testString.length() - returns 7
■
testString.substring(3, 5) – returns the
string “db”
■
testString.contains("oo") – returns
Boolean value true
■
testString.contains("OO") – returns
Boolean value false
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Prewritten Functions Example
▀
How about creating a dice game
■
Ask user if they want to play
■
If yes, generate 2 random numbers
between 1 and 6 to rep the user's
and computer's dice roll
■
Print out numbers and message
saying who won (who got the higher
number) or if it was a tie
■
Ask the user if they want to play
again
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Prewritten Functions Example
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What's the algorithm?
Dice game algorithm
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Then the XD is created
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Prewritten Functions Example
▀
▀
Then an additional requirement is
added to create a function called
getMessage
getMessage will
■
Accept the two dice rolls
■
Generate the correct message
■
Return the message
34
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Prewritten Functions Example
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Dice game pseudocode
▀
Generate the SFC flowchart
SFC flowchart
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Dice Game Example: Raptor
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Raptor returns random number
like java as
■
▀
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A non-Integer between 0 and 1
(exclusive)
So must:
■
Multiply by 6 (max value) to get
number between 0 and 5.99999
■
Then add one to get 1 to 6.9999
■
Then truncate (with floor command)
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to get 1 to 6
Dice Game
Example
37
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Dice Game Example
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38
Dice Game Example When Run
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39
Dice Game Example Java
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40
Dice Game Example Java
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41
Alternative Documentation
▀
IPO (Input Processing Output) Chart
■
▀
Really a table with text (not a chart)
Three columns
■
First column identifies input
■
Second column describes processing
■
Third column identifies output
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IPO Example
▀
getTotalWithTax(String zip, Real
total)
■
Calculates a Sales amount including
tax based on the zip code where the
transaction takes places
■
Reads file for the Sales tax
percentage
43
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IPO Example Pseudocode
Function Real getTotalWithTax(String zip,
Real total)
Declare Real taxRate, useableTaxRate,
totalWithTax
taxRate = Read TaxFile for zip
useableTaxRate = taxRate + 1
totalWithTax = total * useableTaxRate
Return totalWithTax
End Function
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IPO Example
▀
Input
zip: String
Processing
Real useableTaxRate, totalWithTax,
total: Real
taxRate: Real
getTotalWithTax(String zip, Real
total)
Output
totalWithTax
totalWithTax
Read taxRate from TaxFile for zip
useableTaxRate = taxRate + 1
totalWithTax = total * useableTaxRate
▀
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Notice that taxRate considered
input even though not a function
argument
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Points to Remember
▀
▀
▀
Functions are methods/modules
that return values
Lots of prewritten functions that
provide commonly used logic
IPO Charts are an alternative
design/documentation tool
46
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Assignments

Non-Graded
Chap

6 labs 6.1 - 6.3
Graded
Chap
6 lab 6.4
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