Getting User Input. What I can I do now? CS 201F11 M. Wainer

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1 Getting User Input A more flexible and user friendly way of running code would be to allow the program to ask the user for information rather than forcing the user to type in everything as functions and parameters. What I can I do now?

2 Creating a Dialog What is the sale tax % rate? 8 How much was the item? The cost with tax is 10.80

3 Example code: core functionality def costwithtax(taxrate, itemcost): return (1+taxRate/100.0)*itemCost ======= Loading Progam ======= >>> costwithtax(8,10) 10.8 User interaction is through the command area. The core functionality can be wrapped to create an interactive version.

4 pseudo code: interaction #ask user what the tax percentage rate is #save taxrate #ask user what the item cost is #save itemcost answer = costwithtax(taxrate, itemcost) #display answer The JES provides a series of functions for interacting with the user listed under the category Input/Output.

5 code: the interactive version def iacostwithtax(): taxrate = requestnumber("what is the tax percentage rate?") itemcost = requestnumber("what is the item cost?") answer = costwithtax(taxrate,itemcost) showinformation("the total cost with tax is "+str(answer)) JES requestxxx functions pop up a dialog to ask the user for information. They return the information gathered. The JES showinformation function puts up a dialog to pass information onto the user.

6 Running the interactive version

7 Running the interactive version Program requests information Program shows information

8 Running the interactive version User responds to requests by entering info Read information, hit OK when ready

9 Consider Usability Do people commonly want to do def ialoopcostwithtax(): multiple calculations? #while user wants to do another taxrate = requestnumber("what is the tax percentage rate?") itemcost = requestnumber("what is the item cost?") answer = costwithtax(taxrate,itemcost) showinformation("the total cost with tax is "+str(answer)) # ask user if more calculations or quit HCI (Human-Computer Interaction) and Interaction Design, study the interface between humans & computer systems focusing on making applications and devices more useful and user friendly.

10 Coding an Interactive Looping Version Using a while-loop While-loops continue looping through their body code until their loop condition evaluates to False. def ialoopcostwithtax(): another = 1 while another > 0: taxrate = requestnumber("what is the tax percentage rate?") itemcost = requestnumber("what is the item cost?") answer = costwithtax(taxrate,itemcost) answerstr = "The total cost with tax is "+str(answer) another = requestinteger(answerstr+"\n\nanother (1) or quit(0)?")

11 Running the looping interactive version User can repeat w/o having to restart program To reduce the number of dialog boxes, an input box also shows info (answerstr) if another > 0 else loop over line spacing with \n another = requestinteger(answerstr+"\n\nanother (1) or quit(0)?")

12 while loop flowchart Condition is checked before each iteration End No another >0 Yes another = 1 Initialize condition variable(s) While the loop condition is true, enter body of loop Typically change the condition variable(s) within the loop

standard examples: Property Settings, Color Picking, File Picking,

13 Dialog Boxes Most GUI (graphical user interfaces) provide dialog windows as a means of interacting with the user for specific purposes (Some standard examples: Property Settings, Color Picking, File Picking, warnings and error messages etc.) Programmers can create their own custom dialogs.

14 JES Dialog Boxes Request values (input) Show Messages (output) JES provides some simple dialog boxes for interacting with users. More advanced dialog boxes can be created by using various other libraries (like Java Swing).

15 Requesting numerical values floatnum = requestnumber(msg) intnum = requestinteger(msg) Restrict input to integers within a particular range. min max bndintnum = requestintegerinrange("item quantity? (limit 3)",1,3)

16 Requesting & Showing strings itemname = requeststring("item name?") Unlike with printnow(msg), using showinformation(msg) will pause until the user clicks OK iteminfo = "The cost of "+itemname+" with tax is "+str(answer) showinformation(iteminfo) String variables can be used to make long or complex msgs easier

17 Alert Boxes GUI (graphical user interfaces) usually provide special dialog windows to alert users to situations that can take them off of the Happy Path A bad situation may be about to happen. Ideally the user is warned and can take action to avoid problems Something unfortunate has occurred. Ideally this shouldn't happen but sometimes cannot be avoided. showwarning(msg) showerror(msg)

18 Happy Path The Happy Path refers to the normal expected path of execution when there are no errors or unusual circumstances. It is the path that usually comes to mind first and tends to be the easiest to design and program. Danger in failing to realize everything doesn't always go down that straight-forward path.

19 Not so Happy Path Other paths involve errors and special cases and can make the code considerably more difficult to implement correctly. Good code, should be tested and consider at least the likely alternatives to the Happy Path. Even this simple example has the potential to get messy. What happens if the user enters -8 or 0.08? What happens if the Cancel button is hit instead of OK?

20 CS Annual Career Day Event >>> Computer Science Undergraduates & Graduates <<< October 18th(Tuesday) from 4:00-6:00 p.m. at the Campus Lake Boat Dock Pavilion. Paddle boats and refreshments will be available. This event is held in conjunction with Career Services All Majors Fair which will be held from 9:00 a.m.-2:00 p.m. on October 19th in the Student Center. Representatives from computer science related companies will join us. The representatives will introduce themselves and talk about internship and job opportunities which they may have available for students. (There is a growing interest in languages like Python/Jython make sure to mention you're learning it!)

21 Exam 2 Exam 2 is tentatively scheduled for Oct 26, a week from this Wed.

Chapter 3. Iteration

Chapter 3. Iteration Chapter 3 Iteration Iteration Iteration is the form of program control that allows us to repeat a section of code. For this reason this form of control is often also referred to as repetition. The programming