ITBP 119Algorithms and Problem Solving

Section 2.1 Installing software

Section 2.2 First Programs

Section 2.3 Variables

outline

• Installation of the software• Writing you first programs• Doing VS Asking Function• Literals• Assignment Statements

– Variables Declaration and Initialization– Expressions– Variable Naming

• Function Parameter Evaluation

Installing Arachnophilia 4.0

• Make a folder APS under My Documents and use it to store all files for this course.

• Download the zip file Arachnophilia from the Blackboard

• Unzip the file

• Double click on the file arach_full.exe

• Follow the instructions

Installing Arachnophilia 4.0

• Set the preview browser to the internal browser

Creating, editing, previewing HTML files

• Create new HTML page

• edit the title

• Add new header

• Add an image

• Change the size of the image

First Program

• The use of alert and prompt

• Let’s write a program that prompt the user with her name and the computer will greet that name by saying: hello …..

• Remember to be in the frames mode so that you can reduce the amount of typing.

Important concepts

• Script

• Comment

• Alert

• Prompt

• Function parameters

• Function return values

• Java script is case sensitive

Doing Vs. Asking Functions

• alert: alert( “hello World !!!”);– doing function in which you are asking the

function to do some task and return nothing– Void function

• prompt: var age = prompt (“enter your age”, “20”);

– Asking function: in which you are asking the function to do some task and return a value.

– Return values are normally assigned to a variable otherwise it will be discarded.

Doing Vs. Asking Functions

alert ( “ hello World “ ) ;

var age = prompt ( “ enter age: “ , “20” ) ;

parameters

Return value

Function name

voidfunction

prompt ( “ enter age: “ , “20” ) ; Is this wrong?

Literals

• By literal we mean any number, text, boolean or other information that represents a value.

• Example:• “ It’s true that ‘ is a literal”• 2008• “ today is 2 / 9 /2008 “• true• “ this#literal*contains%special@characters “• -12.5• “ here I include double quote \” as part of the literal”

• String Literals are specified in programs with double quotes “”

• Number and boolean literals are NOT specified by double quotes “”.

• Boolean means either true or false value.

Assignment Statements

• var Variable = expression– Variables are named memory cells. – A variable contains a value thus you write

person Hind to indicate that the variable person contains the value "Hind".

HindPersonVariable

Memory location contains the value Hind

Value stored inThe memory location

var person = “Hind” ;

Assignment Statements

• var Variable = expression– Expression: any literal value, or a

mathematical/logical expression.– Example of expressions:

• var X = 10;• var Y = 100;• X + Y• var L = true• var name = “your Name “;• var L2 = X < Y && Y != X ;• var X2 = X * X + Y * Y * Y / 12.3 + 7.4;

Assignment Statements/Evaluation

response = “Samira” ;

message = “hello “ + response ;

message = “Hello “ + response ;Samira

Hello Samira

Samira Hello Samira

responsemessage

RHSLHS

Assignment Evaluation

• The Right Hand side of the assignment is evaluated/calculated first.

• The right hand side value is assigned to the left hand side of the assignment.

• The left hand side of the assignment must be always a variable (or none).– var “xyz” = 12; wrong declaration– var x + 10 = y; wrong declaration

Exercise

• Given the following variablesvar month = “September” ;var year = 2008 ;var day = 2 ;

• Calculate the value of each variable in the following assignment statements.

1. tomorrow = day + 1;2. lastYear = year – 1;3. var date1 = day + month + year ;4. var date2 = day + “ month “ + year;5. date3 = day + month + “ year “;6. date4 = “ day ” + month + year;

Exercise**• Given the following variables

var x = “ hello ” ;var y = 2008 ;var z = 2 ;

• Calculate the value of each variable in the following assignment statements.

1. var w = z + 1;2. y = y / 4 + 7 ;3. y = y – 1;4. var d = x + y ;5. var d2 = x + y + x + “ again ”;6. var d3 = x + “ d2 “;7. z + 1 ; 8. var d4 = z * 5 ;

Assignment Statements

• Which of the following is correct assignment and why?

1. var “salim” = 10;

2. var salim ;

3. var age = 22;var newAge = 11;age + 10 = newAge ;

More about Variables / Variable Names

• Variable Names: the rules of java script state the following about variable names:– The name of the variable cannot be the same

as any of the language keywords.– Variable name can be any sequence of

numeric, alphabet, or the special characters _, $

– Variable name should only start with alphabet ,under score _, or $.

– Variables are case sensitive

Exercise

• Example: identify the correctness of the following variables names.

1. var my_age = 25;2. var _myAge = 22;3. var TODAY = “4/9/2008” ;4. var $amir_ = “ SAMIR” ;5. var alert = 10.43 ;6. var Alert = 10.2 ;7. var prompt = “ prompt me please “;8. var salim%ali = true ;9. var 1foo = false;

Function Parameter Evaluation

• The parameter of a function can be an expression.

• If the parameter is an expression then it is evaluated/calculated first and then it is passed to the function.

Function Parameter Evaluation

• Example:var x =10;

alert( x + 10 );

1. The parameter of the function alert is the expression x + 1.

2. Before the alert is run, the computer computes the value of the expression which is x+1 = 10 + 1 = 11

3. The value 11 is passed to the alert.

Exercise

• Which of the following are literals and which are variables?

1. “Fatima”2. _salim3. dateOfBirth4. 123435. “12343”6. “3.14”7. 12.4232228. Pi

Exercise

• Given the following two variables, what is the difference between the following:

• var name = “zena”

• var friend = “hoda”

name = friend; name = “ friend “;

Initialization and Declaration

• Declaration of a variable: is a way to give a name to some memory location.– Use the keyword var to declare a variable– There will be No initial value in the memory

• Example: variable declarationsvar age ;

var name ;

var firstName, lastName ;

Initialization and Declaration

• Initialization of variable: Storing a value in the variable.– Example:

var age;

var name ;

var firstName, lastName;

age = 10;

name = “Mahir”;

firstName = “Salwa”;

lastName = name;

declarations

initialization

Initialization and Declaration

• We can initialize a variable while declaring it

• Example:var age = 10;

var name = “Mahir” ;

var firstName = “Salwa” , lastName= name ;

Exercises

• What will be the output of the alert function in the following (explain your answers)

…<script>var name = “alia”;alert(name);name =prompt(“ enter name:” , “salma”);alert(name); </script>…

Exercises

• What will be the output of the alert function in the following (explain your answers)

…<script>var name = “alia”;prompt(“ enter name:” , “salma”);alert(name); </script>…

Exercises

• What will be the output of the alert function in the following (explain your answers)

…<script>var name ;var fName=prompt(“ enter name:” , “salma”);alert(name);alert(fName); </script>…

Exercises

• What will be the output of the alert function in the following (explain your answers)

…<script>var fName=prompt(“ enter name:” , “salma”);var msg1 = “hello” + fName;alert( msg1);var msg2 = “welcome “ + “fName” ;alert( msg2);</script>…

Exercises

• What will be the output of the alert function in the following (explain your answers)

…<script>var x = “salam” ;var msg1 = “hello ” + x ;alert( msg1);x = x + “ alaykum “;alert( x);</script>…

Exercises• What will be the output of the alert function in the

following (explain your answers)…<script>var x = 10 ;alert( x);x = x * 10 ;alert( x);x = x / 20;alert(x);</script>…