ITBP 119 Algorithms and Problem Solving Section 2
ITBP 119 Algorithms 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 Function name alert ( “ hello World “ ) ; parameters Return value var age = prompt ( “ enter age: “ , “ 20” ) ; Is this wrong? prompt ( “ enter age: “ , “ 20” ) ;
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” ; Person Variable Hind Memory location contains the value Hind Value stored in The memory location
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 L 2 = X < Y && Y != X ; var X 2 = X * X + Y * Y / 12. 3 + 7. 4;
Assignment Statements/Evaluation response = “Samira” ; message = “hello “ + response ; message = “Hello “ + response ; Hello Samira LHS Samira RHS Samira response Hello Samira 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. 1. 2. 3. 4. 5. 6. tomorrow = day + 1; last. Year = year – 1; var date 1 = day + month + year ; var date 2 = day + “ month “ + year; date 3 = day + month + “ year “; date 4 = “ 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. 2. 3. 4. 5. 6. 7. 8. var w = z + 1; y=y/4+7; y = y – 1; var d = x + y ; var d 2 = x + y + x + “ again ”; var d 3 = x + “ d 2 “; z+1; var d 4 = 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 new. Age = 11; age + 10 = new. Age ;
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. 2. 3. 4. 5. 6. 7. 8. 9. var my_age = 25; var _my. Age = 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 1 foo = 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 • 1. 2. 3. 4. 5. 6. 7. 8. Which of the following are literals and which are variables? “Fatima” _salim date. Of. Birth 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 first. Name, last. Name ;
Initialization and Declaration • Initialization of variable: Storing a value in the variable. – Example: var age; var name ; var first. Name, last. Name; age = 10; name = “Mahir”; first. Name = “Salwa”; last. Name = name; declarations initialization
Initialization and Declaration • We can initialize a variable while declaring it • Example: var age = 10; var name = “Mahir” ; var first. Name = “Salwa” , last. Name= 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 f. Name=prompt(“ enter name: ” , “salma”); alert(name); alert(f. Name); </script> …
Exercises • What will be the output of the alert function in the following (explain your answers) … <script> var f. Name=prompt(“ enter name: ” , “salma”); var msg 1 = “hello” + f. Name; alert( msg 1); var msg 2 = “welcome “ + “f. Name” ; alert( msg 2); </script> …
Exercises • What will be the output of the alert function in the following (explain your answers) … <script> var x = “salam” ; var msg 1 = “hello ” + x ; alert( msg 1); 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> …
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