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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>…