BIT116: ScriptingLecture 05

Conditional Statements

2

Today Quiz

Hand in your jQuery exercises from last lecture They don't have to be 100% perfect to get full credit They do have to be "done except for maybe some small-ish errors"

JavaScript: Conditional Statements

3

Conditional Statements – Basic Syntax

4

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!"

5

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

6

The if Statement (Example)

if (hour < 18){   show = "Good day";}

FILE: Conditional_Demonstration_1.html

7

The if…else Statement (Example)

if (hour < 18){ show = "Good day";}else{ show = "Good evening";}

FILE: Conditional_Demonstration_1.html

8

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!";}

FILE: Conditional_Demonstration_1.html

if (hour < 12){

show = "Good morning";}else

if ( hour < 18 ){

show = "Good afternoon";

}else

if ( hour < 22 ){ show = "Good evening";} else{

show = "Goodnight!";}

9 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

10

Conditional Statements – Effective Usage

11

If:Optional Extra Think of an if as a way of asking if the program shouldoptionally 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 variablevar hour = $("#time");

// ALWAYS tell the user what their choice is:$("#requiredOutput").html("Your time is " + hour);

// OPTIONALLY tell them 'good day'$("#optionalOutput").html("Good day!");

// Is it before 6pm?if (hour < 18)

YES

NO

12

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);

IfElse:Either/Or

// Store time into variablevar hour = $("#time");

// ALWAYS tell the user what their choice is:$("#requiredOutput").html("Your time is " + hour);

// THEN tell them 'good day'$("#additionalOutput").html("Good day!");

// Is it before 6pm?if (hour < 18)

YESNO

// OTHERWISE Tell them 'good evening'$("#additionalOutput").html("Good evening!");

13

Think of an if 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);

Multiway If..Else:Choose One

// ALWAYS tell the user what their choice is:$("#requiredOutput").html("Your time is " + hour);

// Tell them 'good morning'Show = "Good morning";

// What is the hour?

hour< 12

// Tell them 'good day'show = "Good day!";

12 ≤ h< 18

// Tell them 'good evening'show = "Good evening!";

18 ≤ h< 22

// Tell them 'goodnight'show = "Good night!";

hour≥ 22

14

How To Solve Coding Problems1. List the steps that must be done in order to solve the problem

2. 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

3. 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

4. Proofread your solution!!!

5. Code it up

6. Test it out1. Figure out the answer yourself, by hand, then compare to the program

15

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.

16

Example: Fahrenheit Celsius, with bonus commentary! 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:1. First, get input

2. 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.

3. Display results on page

4. Tell'em if it's freezing

5. Tell'em if it's boiling

Try writing this in a flowchart format

Try writing this in pseudocode format (I'll do this in OneNote, so check the after-class videos to see these demonstrated

17

Example: Fahrenheit Celsius, with bonus commentary! 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

18

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

19 Do Exercise#2

20

Example: Grade FeedbackProblem specification:

Create a page that convert a 0-100 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 Error!

21

Example: Grade feedback List steps:

1. First, get input

2. If the grade is negative, display an error and immediately exit/stop/halt/etc.

3. 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 )

4. 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

22

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

23

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)

24 Do Exercise#3