1 intro to programming & algorithm design input validation copyright 2003 by janson industries...

1

Intro to Programming & Algorithm Design

Input Validation

Copyright 2003 by Janson Industries

This presentation can be viewed on line in a file named: ch07.IntrotoProg.InputValidation.ppt

Assg

Copyright 2014 by Janson Industries2

Objectives▀ Explain

■ GIGO (garbage in garbage out)

■ Defensive programming

■ The input validation loop

■ Different types of validation♦ Data type♦ Range♦ Completeness

▀ Show how to code validation functions in Java


GIGO▀ The program can be coded

correctly but if you put bad data in, you will get bad results

▀ This has been the demise a many a new application

■ All coding done and correct but the data conversion wasn't done properly

♦ I.e. the customer db data is incorrect so all the bills are sent to the wrong customers


GIGO▀ Not just true of programs

■ What happens if you put diesel in your car engine?

♦ You had a perfectly good car but then ruined it with bad input

■ That’s why car manufacturers build the car so only the unleaded nozzle fits

♦ That's a form of input validation!


Defensive Programming▀ Only provide valid values that the user

can select from

■ The ubiquitous state abbr list

■ Checkboxes/buttons indicating selected values

♦ I accept the license agreement

▀ Write code to detect all possible data errors and then either

■ Correct the error

■ Inform the user of the error and provide info to help them correct it


Data Errors ▀ Wrong type of data

■ Numbers vs. text♦ For month: "November" vs. 11

■ Integers vs. decimal numbers♦ For month: is 11.53 a valid month

▀ Completeness/invalid size

■ Did the user enter no data or only part of the data

♦ 3224 for a zip code

■ Put in too much data♦ 322456245374835374 for a zip code


Data Errors ▀ Data not within a valid range

■ Month should be between 1 and 12

■ Birthdates should not be over 120 yrs ago

▀ Data not from valid set of values

■ Gender can be "M" or "F"

▀ Data integrity

■ Zip code entered not valid for state abbr entered

■ Customer number entered not valid


Data Validation Pre-test Loop▀ Standard way of making sure data

is valid

■ Prompt user for data

■ Read the data in

■ Have a loop that tests the data validity

■ If not valid♦ Fix data or display a useful message so

the user can fix the data♦ Read the data again


Data Validation Pre-test LoopFunction String getMonth() Declare String month Declare Integer monthNumber // User prompt explains the valid values Display "Enter a month number between 1 and 12" Input month monthNumber = stringToInteger(month) While (monthNumber < 1 OR monthNumber > 12)

Display "Enter a month number. For example, 1 for Jan, 2 for Feb"

Input monthmonthNumber = stringToInteger(month)

End While Return monthEnd Function


monthNumber= stringToInteger(month)

Display “Enter a month number between 1 and 12”

Declare String month

Integer monthNumber

Data Validation Pre-test LoopgetMonth()

Input month


Return month

Input month

While monthNumber<1 OR monthNumber >12

False

Display “Enter a month number. For example, 1 for Jan, 2 for Feb"

monthNumber= stringToInteger(month)

True


Data Validation Loop▀ How could we have fixed the data

for the user?

■ Check to see if the three character abbr or full text for the month was entered

♦ If so, change to the correct number

■ Check to see if a space(s) was entered at the beginning or end of the text

♦ If so, trim the space(s) off


Data Validation Post-test Loop▀ Start loop

■ Prompt the user for the data

■ Read the data in

▀ End of loop validity test, if not valid, go to the start of the loop

▀ A lot less code but only one prompt/msg to the user

■ No useful error msg with further info


Data Validation Post-test Loop

Function String getMonth() Declare String month Declare Integer monthNumber Do // User prompt explains the valid values Display "Enter a month number between 1 and 12" Input month monthNumber = stringToInteger(month) While (monthNumber < 1 OR monthNumber > 12) Return monthEnd Function


Data Validation Post-test Loop


Validation Functions▀ For data that is commonly input, create validation

functions that many programs can use

■ Many programs may ask for the month

■ Have a common function to get data and do all the validation

■ Advantage: only written once♦ Less coding♦ If need to change, change in only one place


MyUtils


MyUtils▀ Any program that requests a date can

now use the day and month functions

public class Test {

public static void main(String[] args) {String month = null, day = null;int monthNumber = 0;month = MyUtils.getMonth();monthNumber = Integer.valueOf(month);day = MyUtils.getDay(monthNumber);MyUtils.p("The date entered is " + month + "/" +

day); }}


Validating Strings▀ Added problem of lower and upper case

▀ "yes", "YES", "Yes", "yEs" are all different values

▀ Easiest solution is to change input to either upper or lower case then test for the value


Validating Strings▀ Restaurant is asking customer for items they want (pizza, soda, calzone, etc.) and sizes

▀ Need to validate both the item and size

▀ Since the sizes (small, medium, and large) are the same for all items will create a common getSize function


Validating Strings▀ getSize will also check to see if the user enters "s", "m", or "l"

■ If so will convert to "small", "medium" or "large"

▀ In case of a typo ("meduim", "larj", "smal", etc.) will check the first letter

■ if "s", "m", or "l", will convert to "small", "medium" or "large"


String Validationmain() Declare String item, size; Display "Enter the item you want to purchase: Pizza, Calzone or Soda" Input item item = toLower(item) While (item != "pizza" AND item != "calzone" AND item != "soda")

Display "Please enter Pizza, Calzone or Soda " Input item item = toLower(item) End While size = getSize(item) Display "You have ordered a ", size, " ", itemEnd


String Validation

Function String getSize(String item)

Declare String size

// User prompt asks for size Display "Enter the size ", item, " you would like" Input size size = toLower(size)

While (size != "small" AND size != "medium" AND size != "large")


If (substr(size, 0 , 1) = "s" OR substr(size, 0, 1) = "m" OR substr(size, 0, 1) = "l" Then If substr(size, 0 , 1) = "s" Then

size = "small" Else If substr(size, 0 , 1) = "m" Then

size = "medium" Else

size = "large" End If

End IfElse Display "Enter small, medium, or large" Input size size = toLower(size)

End While Return sizeEnd Function 24

String Validation


Flow Chart - SFC


Flow Chart - SFCFlow Chart - SFC


Flow Chart - SFC


Flow Chart - Raptor▀ Raptor cannot convert strings to

upper or lower case

▀ However, we can write a function to do it

▀ All characters can be represented as numbers

▀ In ASCII, A-Z are 65-90 and a-z are 97-122


ASCII Chart


Flow Chart - Raptor▀ Raptor can return the number

associated with a particular character or visa versa

■ charNum = to_ascii('A')♦ charNum will equal 65

■ char = to_character(97)♦ char will equal 'a'

▀ You can manipulate a character value as if it were a number■ Add 32 to get lower case character


Flow Chart - Raptor▀ Raptor cannot perform a true

substring function

▀ Can identify a single character within a string by specifying the index of the character

▀ Assuming address = "1 Main St"■ address[3] is "M"■ address[7] is " "


Flow Chart - Raptor▀ When an index is used, value

type is character NOT string■ Comparing two different value

types can't be done♦ 123 = "123" is invalid

■ Or in this case♦ address[3] = "M" is invalid♦ However, address[3] = 77 is valid

▀ Could also create a character variable with the value "M"■ charVar = to_character[77]


toLowerCaseFunction String toLowerCase(String stringToChange)

Declare Integer ctr = 1

While ctr <= length(stringToChange)

If stringToChange[ctr] > 64 AND stringToChange[ctr] < 91 stringToChange[ctr] = stringToChange[ctr] + 32

End If

ctr = ctr + 1 End While

Return stringToChange

End Function


Start

ctr ← 1

ctr > length_of(stringToChange)

stringToChange[ctr] > 64 && stringToChange[ctr] < 91

stringToChange[ctr] ← stringToChange[ctr] + 32

NoYes

ctr ← ctr + 1

End

Yes

No

Loop

//Declare variablesInteger ctr

35

Raptor toLowerCase()

Notice how character value treated like a

number

Had to change loop condition because of

Raptor


Start

"Enter the item you want to purchase: Pizza, Calzone or Soda"GET stringToChange

toLowerCase

item ← stringToChange

item = "pizza" OR item = "calzone" OR item = "soda"

"Please enter Pizza, Calzone or Soda"GET stringToChange

toLowerCase


getSize

PUT "You have ordered a " + size + " " + item¶

End

Yes

No

Loop

//Declare variablesString item, size, stringToChange

36

Raptor main()


Start

"Enter the item you want to purchase: Pizza, Calzone or Soda"GET stringToChange

toLowerCase


item = "pizza" OR item = "calzone" OR item = "soda"

"Please enter Pizza, Calzone or Soda"GET stringToChange

toLowerCase


getSize

PUT "You have ordered a " + size + " " + item¶

End

Yes

No

Loop

//Declare variablesString item, size, stringToChange

37


Raptor getSize()

Start

"Enter the size " + item + " you would like"GET stringToChange

toLowerCase

size ← stringToChange

size = "small" OR size = "medium" OR size = "large"

size[1] = to_character(115) OR size[1] = to_character(109) OR size[1] = to_character(108)

size[1] = to_character(115)

size ← "small" size[1] = to_character(109)

size ← "medium" size ← "large"

NoYes

NoYes"Enter small, medium, or large"GET stringToChange

toLowerCase


NoYes

End

Yes

No

Loop


Raptor getSize()

Start

"Enter the size " + item + " you would like"GET stringToChange

toLowerCase


size = "small" OR size = "medium" OR size = "large"

size[1] = 115 OR size[1] = 109 OR size[1] = 108

size[1] = 115

size ← "small" size[1] = 109

size ← "medium" size ← "large"

NoYes

NoYes"Enter small, medium, or large"GET stringToChange

toLowerCase


NoYes

End

Yes

No

Loop

Again, notice how character value treated

like a number


When GetItem run


PIAZZ changed to piazz

Prompted for valid item


Pizza changed to

pizza

Prompted for a size


LARJ changed to larj and size set to large

Message displayed


Java▀ Does have a toLowerCase

method■ So we don't have to mathematically

manipulate the ASCII integer values

▀ Also has an equalsIgnoreCase method■ String name = "MOE";■ name.equalsIgnoreCase("moe");

♦ Is true


Java GetItem

Uses toLowerCase

Negative logic (!) in while


Java getSize

Uses the substring function


Bad values caught and corrected

Java GetItem


Reading Mixed Data Java lets you read individual

values not just the whole line next() gets all text on a line up to the

next space

nextInt() gets all text up to the next space and converts it to an integer

nextDouble() gets all text up to the next space and converts it to a double

None of these advance the cursor to the next line!


Processing Data Not nitpicking! If entered the

following budget data

And you tried to process with these statements

Rent500Car280

item1 = keyboard.nextLine();item1Amount = keyboard.nextInt();item2 = keyboard.nextLine();item2Amount = keyboard.nextInt();


Processing Data There would be an

InputMismatchException the second time nextInt executed

WHAAAAAAAT!! Must show where cursor is after

each statement executed to understand

First nextLine() reads "Rent" and places cursor at the beginning of the second line


Processing Data When nextInt executed 500 read

and cursor placed at end after the second 0

When the second nextLine (3rd read) executed, it reads the rest of the second line A big fat null

Rent500Car280

Cursor after first read

Cursor after second

read


Processing Data And cursor placed at

beginning of third line

Now when second nextInt executed InputMismatchException

Tries to convert "Car" into a int

Rent500Car280

Cursor after 3rd read

(2nd nextLine)


Processing Data Solution:

Execute another nextLine after the nextInt

Forces the cursor to the line after the line with the int value

item1 = keyboard.nextLine();item1Amount = keyboard.nextInt();keyboard.nextLine();item2 = keyboard.nextLine();item2Amount = keyboard.nextInt();


Points to Remember▀ Bad input will make an

application yield incorrect results

▀ Defensive programming consists of many techniques used to stop bad input

▀ All character data can be represented as an integer value


Assignments Non-Graded

Chap 7 labs 7.1-7.4

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Graded

Chap 7 lab 7.5

55

1 intro to programming & algorithm design input validation copyright 2003 by janson industries...

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