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Introduction to Computing

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Introduction to Computing ­ CS101
VU
LESSON 23
FLOW CONTROL & LOOPS
(Web Development Lesson 8)
During the last Lesson we had a discussion on Data Types, Variables & Operators
We found out about JavaScript data types
About variables and literals
We also discussed several operators supported by JavaScript
JavaScript Data Types
JavaScript recognizes & distinguishes among the following types of values:
Numbers
Booleans
Strings
Undefined
Variables
Variables give us the ability to manipulate data through reference instead of actual valueVariables are
containers that hold values
Declaring Variables
Although JavaScript allows variable declaration, it does not require it - except in the case when we want
to declare a variable being local (more on local variables later in the course!)
JavaScript Variables are Dynamically Typed
Any variable in JavaScript can hold any type of value, and the that type can change midway through the
program
FLOW CONTROL
Select between alternate courses of action depending upon
the evaluation of a condition
condition
True
False
statement
statement
block 1
block 2
JavaScript Flow Control Structures
·
if ... else
·
switch
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Introduction to Computing ­ CS101
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if: Example 1
if ( day == "Sunday" )
bhola = "Cool" ;
semicolon
The condition
Set the value of the variable `bhola to `Cool'
enclosed in
if the `day' is equal to `Sunday'
This was the case if we want to execute a single statement
given that the condition is true
What if we want to execute multiple statements in case the
if: Example 2
if ( day == "Sunday" )
{
bhola = "Cool" ;
mood = "Great" ;
clothing = "Casual" ;
}
if: Example 2
Set the value of the variable
These curly braces group the
multiple statements into a single
`bhola to `Cool', `mood' to `Great',
compound statement
and `clothing' to `casual' if the
if ( day == "Sunday" ) {
bhola = "Cool" ;
mood = "Great" ;
Note: No
clothing = "Casual" ; semicolon after
the closing curly
}
brace
Set the value of the variable `status' to `Cool',
`mood' to `Great', and `clothing' to `casual' if the
`day' is equal to `Sunday'
Compound Statements
·
At times, we need to put multiple statements at
places where JavaScript expects only oneFor
those situations, JavaScript provides a way of
grouping a number of statements into a
2.
This is done simply by enclosing any number
of statements within curly braces, {
}NOTE: Although the statements
within the block end in semicolons,
the block itself doesn't
if: Example 3
if ( (day == "Sunday") || (day == "Saturday") ) {
bhola = "Cool" ;
mood = "Great" ;
clothing = "Casual" ;
}
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Introduction to Computing ­ CS101
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if: Example 4
weekend = ( day == "Sunday" ) || ( day ==
"Saturday" ) ;
if ( weekend ) {
bhola = "Cool" ;
mood = "Great" ;
What is the data
clothing = "Casual" ;
type of the variable
}
"weekend"?
We now know how to execute a statement or a block of statements given
that the condition is true
What if we want to include an alternate action as well, i.e. a statement or
a block of statements to be executed in case the condition in not true
if ... else: Example 1
if ( GPA >= 1.0 )
bhola = "Pass" ;
else
bhola = "Fail" ;
if ... else: Example 2
if ( GPA >= 1.0 ) {
bhola = "Pass" ;
}
Else
bhola = "Fail" ;
if ... else: Example 3
if ( GPA >= 1.0 ) {
bhola = "Pass" ;
mood = "Great"
;
} else
if ... else: Example 4
if ( GPA >= 1.0 ) {
bhola = "Pass" ;
mood = "Great" ;
} else {
bhola = "Fail" ;
mood = "Terrible" ; }
if ... else: Example 5
This piece of
code is correct,
but not very
if ( grade == "A" )
efficient!
points = 4.0 ;
if ( grade == "B" )
points = 3.0 ;
What can we do
if ( grade == "C" )
to improve it?
points = 2.0 ;
if ( grade == "D" )
points = 1.0 ;
if ( grade == "F" )
points = 0 0 ;
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Introduction to Computing ­ CS101
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if ... else: Example 5
if ( grade == "A" )
This piece of
code is correct,
points =
but not very
4.0 ;
efficient!
if ( grade == "B" )
points =
3.0 ;
What can we do to
if ( grade == "C" )
improve it?
points =
2.0 ;
if ( grade == "D" )
points =
if ... else:
10;
Example 6
if ( grade == "A" )
points = 4.0 ;
else {
if ( grade == "B" )
points = 3.0 ;
else {
if ( grade == "C" )
points = 2.0 ;
else {
if ( grade == "D" )
points = 1.0 ;
else
points = 0.0 ;
}
}
}
switch ( grade ) {
case "A" :
switch:
points = 4.0 ;
A colon
Example 1
break ;
following the
case "B" :
case label is
points = 3.0 ;
required
break ;
case "C" :
points = 2.0 ;
break ;
case "D" :
points = 1.0 ;
break ;
default :
points = 0.0 ;
}
The expression
enclosed in
parentheses is
evaluated and matched
with case labels
This is a case
label
This `break' statement
is the exit point
The `default' statement acts like the
`else' clause in the `if...else'
structure
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Switch Example 2
switch: Example 2
switch ( inquiry ) {
case "apple" :
document.write( "Apples are Rs 50/kg" ) ;
break ;
case "mangos" :
document.write( "Mangos are Rs 90/kg" ) ;
break ;
case "grapes" :
document.write( "Grapes are Rs 60/kg" ) ;
break ;
default :
document.write( inquiry + "? Please retry!" ) ;
}
if...else --?-- switch
·
If the action to be taken of the value of a single variable (or a
single expression), use `switch'
·
When the action depends on the values of multiple variables
(or expressions), use the `if...else' structure
if ... else: Example 7
if ( ( GPA >= 1.0 ) && ( attendance >= 40 ) )
bhola = "Pass" ;
else {
if ( ( GPA >= 2.0 ) && ( attendance >= 36 ) )
bhola
= "Probation" ;
else
bhola = "Fail" ;
LOOPS
}
Loop through a set of statements as long as a condition
is true
True
statement
condition
block
False
JavaScript's Looping Structures
while
for
Virt... l University of Pakistan
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Introduction to Computing ­ CS101
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Decimal to Binary Conversion in JavaScript
x = 75 ;
// x is the decimal number
y = "" ;// y is the binary equivalent
while ( x > 0 ) {
The condition
remainder = x % 2 ;
enclosed in
quotient = Math.floor( x / 2 ) ;
parentheses
y = remainder + y ;
x = quotient ;
}
document.write( "y = " + y ) ;
while: Example 2
while ( tankIsFull == false ) {
tank = tank + bucket ;
}
document.write ( "Tank is full now" ) ;
while: Example 3
x=1;
while ( x < 6000 ) {
document.write ( x ) ;
x=x+1;
}
for: Example 1
Operation
Initial count
Condition
for ( x = 1 ;  x < 6000 ;  x = x + 1 ) {
document.write ( x ) ;
}
for: Description (1)
·
The `for' loop starts by initializing the counter variable (which in this case is
x)
·
The initial value in this case is `1', but can be any other positive or negative
number as well
·
Next the `for' loop checks the condition. If the condition evaluates to a `true'
value, the `for' loop goes through the loop once
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Introduction to Computing ­ CS101
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for: Description (2)
·
After reaching the end of that iteration, the `for' loop goes to the top once
again, performs the operation, checks the condition
·
If the condition evaluates to a `false' value, the `for' loop finishes looping
·
Otherwise, the `for' loop goes through the loop once again
·
Repeat from step 4
for: Example 2
for ( x = 99 ; x < 6000 ; x = x + 1 ) {
document.write ( x ) ;
}
for: Example 3
for ( x = 6000 ; x > 0 ; x = x - 1 ) {
How many iterations would
document.write ( x ) ;
this `for' loop run for?
}
6000?
for: Example 3
How many iterations
for ( x = 6000 ; x > 0 ; x = x - 1 ) {
would this `for' loop run
document.write ( x ) ;
for?
}
6000?
for: Example 4
for ( x = 6000 ; x < 0 ; x = x - 1 ) {
How many iterations
document.write ( x ) ;
would this `for' loop run
}
for?
for --?-- while
None?
·
When the exact number of iterations is known, use the
`for' loop
`for' loops become especially useful when used in conjunction with
arrays
We'll find out about arrays next time, and we'll probe their
usefulness as part of `for' loop structures
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Introduction to Computing ­ CS101
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During Today's Lesson ...
We discussed the concept of flow control using the "if" and "switch" structures
And also the concept behind the "while" and "for" looping structures
We also solved simple problems using flow control and loop structures
Next (the 9th) Web Dev Lecture:
Arrays
We will find out why we need arrays
We will become able to use arrays for solving simple problems
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Table of Contents:
  1. INTRODUCTION
  2. EVOLUTION OF COMPUTING
  3. World Wide Web, Web’s structure, genesis, its evolution
  4. Types of Computers, Components, Parts of Computers
  5. List of Parts of Computers
  6. Develop your Personal Web Page: HTML
  7. Microprocessor, Bus interface unit, Data & instruction cache memory, ALU
  8. Number systems, binary numbers, NOT, AND, OR and XOR logic operations
  9. structure of HTML tags, types of lists in web development
  10. COMPUTER SOFTWARE: Operating Systems, Device Drivers, Trialware
  11. Operating System: functions, components, types of operating systems
  12. Forms on Web pages, Components of Forms, building interactive Forms
  13. APPLICATION SOFTWARE: Scientific, engineering, graphics, Business, Productivity, Entertainment, Educational Software
  14. WORD PROCESSING: Common functions of word processors, desktop publishing
  15. Interactivity to Forms, JavaScript, server-side scripts
  16. ALGORITHMS
  17. ALGORITHMS: Pseudo code, Flowcharts
  18. JavaScript and client-side scripting, objects in JavaScript
  19. Low, High-Level, interpreted, compiled, structured & object-oriented programming languages
  20. Software Design and Development Methodologies
  21. DATA TYPES & OPERATORS
  22. SPREADSHEETS
  23. FLOW CONTROL & LOOPS
  24. DESIGN HEURISTICS. Rule of thumb learned through trial & error
  25. WEB DESIGN FOR USABILITY
  26. ARRAYS
  27. COMPUTER NETWORKS: types of networks, networking topologies and protocols
  28. THE INTERNET
  29. Variables: Local and Global Variables
  30. Internet Services: FTP, Telnet, Web, eMail, Instant messaging, VoIP
  31. DEVELOPING PRESENTATIONS: Effective Multimedia Presentations
  32. Event Handlers
  33. GRAPHICS & ANIMATION
  34. INTELLIGENT SYSTEMS: techniques for designing Artificial Intelligent Systems
  35. Mathematical Functions in JavaScript
  36. DATA MANAGEMENT
  37. DATABASE SOFTWARE: Data Security, Data Integrity, Integrity, Accessibility, DBMS
  38. String Manipulations:
  39. CYBER CRIME
  40. Social Implications of Computing
  41. IMAGES & ANIMATION
  42. THE COMPUTING PROFESSION
  43. THE FUTURE OF COMPUTING
  44. PROGRAMMING METHODOLOGY
  45. REVIEW & WRAP-UP of Introduction to Computing