1. BIT116: Scripting Lecture 05
Conditional Statements

2. Today Quiz JavaScript: Conditional Statements
Today’s quiz is on debugging
Next lecture we’re going to start with ‘fill in blank boxes’ quizzes’
I’ve got a ‘sample quiz’ up front: it doesn’t count for points, but it’ll be a good example of what to expect going forwards
JavaScript: Conditional Statements

3. Due Today Assignment 1 If you’re having trouble:
You can submit a 1 page essay about what you tried to do, how it worked out, and what you can do differently in the future in order to get an extra revision
Focus on constructive advice about stuff you control.
Include the essay (.DOCX or .PDF) in your .ZIP

4. Conditional Statements – Basic Syntax

5. What is a Conditional Statement?
A conditional statement is a statement that you can use to execute a bit of code based on a condition or to do something else if that condition is not met. You can think of a conditional statement as being a little like cause and effect.
Here's an example:
"If a variable named myMoney is greater than 1000, send an alert that says my finances are OK. Otherwise, send an alert saying I need more money!"

6. The if , if/else , if/else if/else Statements
if statement: use this statement to execute some code once only if a specified condition is true
if...else statement: use this statement to execute some code if the condition is true and another code if the condition is false
if...else if....else statement: use this statement to select one of many blocks of code to be executed

7. FILE: Conditional_Demonstration_1.html
The if Statement (Example)
if (hour < 18) {    show = "Good day"; }
FILE: Conditional_Demonstration_1.html

8. FILE: Conditional_Demonstration_1.html
The if…else Statement (Example)
if (hour < 18) {
show = "Good day"; }
else
show = "Good evening";
FILE: Conditional_Demonstration_1.html

9. FILE: Conditional_Demonstration_1.html
The if…else if…else Statement (Example)
if (hour < 12) {
show = "Good morning"; }
else if ( hour < 18 )
show = "Good afternoon";
else if ( hour < 22 )
show = "Good evening";
else
show = "Goodnight!";
if (hour < 12) {
show = "Good morning"; }
else
if ( hour < 18 )
show = "Good afternoon";
if ( hour < 22 )
show = "Good evening";
show = "Goodnight!";
FILE: Conditional_Demonstration_1.html

10. Do Exercise #1
The objective is to remind yourself what to type in order to get an if, if/else, or multiway if…else to work

11. Conditional Statements – Effective Usage

12. If:Optional Extra YES NO
Think of an if as a way of asking if the program should optionally do something extra, then resume the program
var hour = $("#time");
if (hour < 18) {    $("#optionalOutput").html( "Good day!"); }
$("#requiredOutput").html("Your time is " + hour);
// Store time into variable
var hour = $("#time");
// Is it before 6pm?
if (hour < 18)
YES
// OPTIONALLY tell them 'good day'
$("#optionalOutput").html("Good day!"); NO
// ALWAYS tell the user what their choice is:
$("#requiredOutput").html("Your time is " + hour);

13. IfElse: Either/Or NO YES If/Else: Either do A or else do B
One and only one will happen!
var hour = $("#time");
if (hour < 18) {    $("#additionalOutput").html("Good day!"); }
else {
   $("#additionalOutput").html("Good evening!"); }
$("#requiredOutput"). html("Your time is " + hour);
// Store time into variable
var hour = $("#time"); NO
// Is it before 6pm?
if (hour < 18)
YES
// THEN tell them 'good day'
$("#additionalOutput").html("Good day!");
// OTHERWISE Tell them 'good evening'
$("#additionalOutput").html("Good evening!");
// ALWAYS tell the user what their choice is:
$("#requiredOutput").html("Your time is " + hour);

14. Multiway If..Else: Choose One
Think of a multiway if…else as a way of asking if the program should exactly one of a several possible choices
if (hour < 12) { show = "Good morning"; } else if ( hour < 18 ) { show = "Good afternoon"; } else if ( hour < 22 ) { show = "Good evening"; } else { show = "Goodnight!"; }
$("#requiredOutput").html("Your time is " + hour);
// What is the hour?
hour< 12
// Tell them 'good morning'
Show = "Good morning";
12 ≤ h< 18
// Tell them 'good day'
show = "Good day!";
18 ≤ h< 22
// Tell them 'good evening'
show = "Good evening!";
hour≥ 22
// Tell them 'goodnight'
show = "Good night!";
// ALWAYS tell the user what their choice is:
$("#requiredOutput").html("Your time is " + hour);

15. How To Solve Coding Problems
List the steps that must be done in order to solve the problem
Identify those steps that are OPTIONAL, EITHER-OR, or CHOOSE ONE (FROM MANY)
These will be your if, if…else, and multiway if…else's
Sketch out you’re your solution
You can use flowcharts, like we did on the prior slides
You can use pseudocode, which is easier to write into comments in your source code file
Proofread your solution!!!
Code it up
Test it out
Figure out the answer yourself, by hand, then compare to the program

16. Example: Fahrenheit  Celsius, with bonus commentary!
Problem specification: Create a page that will convert from Fahrenheit to Celsius. In addition, if the temperature is below freezing you should display a message formatted to look 'chilly'. Similarly, display a 'toasty' looking message if the temperature is above boiling.

17. Example: Fahrenheit  Celsius,
I'll assume that you can set up the HTML and basic jQuery stuff on your own. We're just focus on the problem-specific stuff
List steps:
First, get input
Next, run through formula
NOTE: You will probably need to look this up. Looking it up is something you need to do, not something that the program does.
Display results on page
Tell'em if it's freezing
Tell'em if it's boiling
Try writing this in a flowchart format
Try writing this in pseudocode format

18. Example: Fahrenheit  Celsius,
Once you've thought the problem through (listing, flowchart/pseudocode), then code it up!
Test
Remember: Calculate the answer yourself, then compare it to your program
Try several temperatures between freezing & boiling
If you don't remember it off-hand then look up for yourself what these are in Fahrenheit
Try freezing exactly, then one degree above and one degree below
Does the 'chilly' message show up correctly?
Try boiling exactly, then one degree above and one degree below
Does the 'toasty' message show up correctly?
Are there any other problems with this?
FILE: F2C.html

19. Close, but not quite 
If we put in 300 & click we get the 'hot' message. If we then change it to 3 & click we see BOTH messages
We'll fix this with an if…else
FILE: F2C_IfElse.html

20. Do Exercise #2

21. Example: Grade Feedback
Problem specification: Create a page that convert a numeric grade into an 'A', 'B', 'C', 'D', or 'F' grade, based on the table to the right. If a number greater than 100 or less than zero is used then display an error message on the page.
Numeric Grade
Letter Grade
>100
Error!
90 – 100 A
80 – 90 B
70 – 80 C
60 – 70 D
0 – 60 F
< 0

22. Example: Grade feedback
List steps:
First, get input
If the grade is negative, display an error and immediately exit/stop/halt/etc.
If the grade is >100, display an error and immediately stop. (If we make it past this step then the input must be ok) (mostly – we're assuming that it's a number  )
Use a multiway if/else to figure out which letter grade they're getting
Let's try writing this in a flowchart format
Let's try writing this in pseudocode format
(I'll do this in OneNote, so check the after-class videos to see these demonstrated)
Useful idea: 'Peeling off' errors 'Peeling away' cases

23. Example: Grade feedback
Once you've thought the problem through (listing, flowchart/pseudocode), then code it up!
Test
Remember: Calculate the answer yourself, then compare it to your program
Try it with 95, 90, 100
Try it with 85, 80, 90
Etc, etc
Try it with 101, 110, 200
Try it with 0, -1, -10
Are there any other problems with this?
FILE: GradeFeedback.html

24. Ideas / Interests for in-class exercises?
A research paper that I read said that it's good to give new programmers a wider choice of exercises
So instead of "do #1, then #2, then #3"…
Instead tell people "Here's 6, pick 3"
This isn't always appropriate…
"Let's make sure you can type in the syntax"
Mechanical things like "ID different regions as CSS/JS"
… and I'm not 100% confident I can brainstorm a zillion exercises for each class, but I'm gonna try it
What ideas/interests do you have that might make for interesting problems involving if or if/else statements?
I don't guarantee I'll use them, but it'll help
Think about this during class, and we'll brainstorm a list towards the end (or else at the start of next class)

25. Do Exercise #3