Intro to Programming & Algorithm Design 4/17/2017 Intro to Programming & Algorithm Design Input Validation Assg This presentation can be viewed on line in a file named: ch07.IntrotoProg.InputValidation.ppt Copyright 2003 by Janson Industries

Objectives Explain Show how to code validation functions in Java 4/17/2017 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

4/17/2017 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 4/17/2017 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 4/17/2017 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 Completeness/invalid size 4/17/2017 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 4/17/2017 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 4/17/2017 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 Loop 4/17/2017 Data Validation Pre-test Loop Function 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" End While Return month End Function

Data Validation Pre-test Loop 4/17/2017 Data Validation Pre-test Loop getMonth() Declare String month Integer monthNumber Display “Enter a month number between 1 and 12” Input month monthNumber= stringToInteger(month)

While monthNumber<1 OR monthNumber >12 4/17/2017 False While monthNumber<1 OR monthNumber >12 True Display “Enter a month number. For example, 1 for Jan, 2 for Feb" Input month monthNumber= stringToInteger(month) Return month

Data Validation Loop How could we have fixed the data for the user? 4/17/2017 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 4/17/2017 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 4/17/2017 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 month End Function

Data Validation Post-test Loop 4/17/2017 Data Validation Post-test Loop

4/17/2017 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

4/17/2017 MyUtils

4/17/2017 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 4/17/2017 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

4/17/2017 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

4/17/2017 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 Validation main() Declare String item, size; 4/17/2017 String Validation main() 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 " End While size = getSize(item) Display "You have ordered a ", size, " ", item End

String Validation Function String getSize(String item) 4/17/2017 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")

String Validation If (substr(size, 0 , 1) = "s" OR substr(size, 0, 1) 4/17/2017 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 Display "Enter small, medium, or large" Input size size = toLower(size) End While Return size End Function String Validation

4/17/2017 Flow Chart - SFC

4/17/2017 Flow Chart - SFC Flow Chart - SFC

4/17/2017 Flow Chart - SFC

Flow Chart - SFC 4/17/2017

4/17/2017 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 4/17/2017 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 4/17/2017 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 " "

4/17/2017 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]

toLowerCase Function String toLowerCase(String stringToChange) 4/17/2017 toLowerCase Function 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

Raptor toLowerCase() Had to change loop condition because of Raptor 4/17/2017 Had to change loop condition because of Raptor Notice how character value treated like a number

4/17/2017 Raptor main() Notice stringToChange retrieved, toLowerCase invoked, then we have to place stringToChange value into item.

4/17/2017

4/17/2017 Raptor getSize()

Again, notice how character value treated like a number 4/17/2017 Raptor getSize() Again, notice how character value treated like a number

4/17/2017 When GetItem run

Prompted for valid item 4/17/2017 PIAZZ changed to piazz Prompted for valid item

Pizza changed to pizza Prompted for a size 4/17/2017 Pizza changed to pizza Prompted for a size

LARJ changed to larj and size set to large 4/17/2017 LARJ changed to larj and size set to large Message displayed

Java Does have a toLowerCase method 4/17/2017 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

Negative logic (!) in while 4/17/2017 Java GetItem Uses toLowerCase Negative logic (!) in while

Uses the substring function Java getSize 4/17/2017 Uses the substring function

Bad values caught and corrected 4/17/2017 Java GetItem Bad values caught and corrected

Reading Mixed Data 4/17/2017 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 4/17/2017 Not nitpicking! If entered the following budget data And you tried to process with these statements Rent 500 Car 280 item1 = keyboard.nextLine(); item1Amount = keyboard.nextInt(); item2 = keyboard.nextLine(); item2Amount = keyboard.nextInt();

Processing Data 4/17/2017 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

Cursor after first read Cursor after second read Processing Data 4/17/2017 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 Rent 500 Car 280 Cursor after first read Cursor after second read

Processing Data And cursor placed at beginning of third line 4/17/2017 And cursor placed at beginning of third line Now when second nextInt executed InputMismatchException Tries to convert "Car" into a int Rent 500 Car 280 Cursor after 3rd read (2nd nextLine)

Processing Data Solution: Execute another nextLine after the nextInt 4/17/2017 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();

4/17/2017 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 Graded Chap 7 labs 7.1-7.4 4/17/2017 Assignments Non-Graded Chap 7 labs 7.1-7.4 The Word doc is very large, you must delete the video links or the email will be blocked Graded Chap 7 lab 7.5