ITBP 119 Algorithms and Problem Solving

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 void function alert ( “ hello World “ ) ; parameters Function name Return value var age = prompt ( “ enter age: “ , “20” ) ; 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". var person = “Hind” ; Value stored in The memory location Hind Person Variable Memory location contains the value 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 RHS LHS Samira Hello Samira response message

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 variables var month = “September” ; var year = 2008 ; var day = 2 ; • Calculate the value of each variable in the following assignment statements. • tomorrow = day + 1; • lastYear = year – 1; • var date1 = day + month + year ; • var date2 = day + “ month “ + year; • date3 = day + month + “ year “; • 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. • var w = z + 1; • y = y / 4 + 7 ; • y = y – 1; • var d = x + y ; • var d2 = x + y + x + “ again ”; • var d3 = x + “ d2 “; • z + 1 ; • var d4 = z * 5 ;

Assignment Statements • Which of the following is correct assignment and why? • var “salim” = 10; • 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. • var my_age = 25; • var _myAge = 22; • var TODAY = “4/9/2008” ; • var $amir_ = “ SAMIR” ; • var alert = 10.43 ; • var Alert = 10.2 ; • var prompt = “ prompt me please “; • var salim%ali = true ; • 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 ); • The parameter of the function alert is the expression x + 1. • Before the alert is run, the computer computes the value of the expression which is x+1 = 10 + 1 = 11 • The value 11 is passed to the alert.

Exercise • Which of the following are literals and which are variables? • “Fatima” • _salim • dateOfBirth • 12343 • “12343” • “3.14” • 12.423222 • 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 declarations var 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> …

ITBP 119 Algorithms and Problem Solving