Chapter%208:%20Introduction%20to%20High-level%20Language%20Programming

1
Chapter 8 Introduction to High-level Language
Programming

• Invitation to Computer Science,
• C Version, Third Edition

2
Objectives

• In this chapter, you will learn about
• High-level languages
• Introduction to C
• Data types
• Statement types
• Putting the pieces together

3
Objectives

• Managing complexity
• Object-oriented programming
• Graphical programming
• The big picture software engineering

4
Where Do We Stand?

• Early days of computing
• Programmers were satisfied with assembly language
• Programs written by technically oriented people
• Later decades
• Programmers demanded a more comfortable
  programming environment
• Programs could be written by nontechie people

5
High-level Languages

• High-level programming languages
• Called third-generation languages
• Overcame deficiencies of assembly language
• Programmer didnt need to manage details of data
  storage or movement

6

• Figure 8.1
• Transitions of a High-level Language Program

7
Simple C Program

• / Get a number input from the user and print it
  out /
• include ltiostreamgt
• using stdcout
• using stdcin
• int main()
• // Prompt user, define a variable for num, input
  a value.
• cout ltlt "Please input an integer "
• int num
• cin gtgt num
• // Output result
• cout ltlt "The number you entered"
• cout ltlt " is " ltlt num ltlt "\n"
• return 0

8
Overall Form of a Typical C Program

• prologue Comment (optional)
• include directives (optional)
• using directives (optional)
• functions (optional)
• main function declarations (optional) main
  function body

9
Introduction to C

• Some components of program in Figure 8.2
• Comments
• Give information to human readers of code
• Include directive
• The linker includes object code from a library
• Using directive
• Tells compiler to look in a namespace for
  definitions not mentioned in the program

10
Data Types

• Identifiers names in a programming language
• Keywords have special meanings in C
• C case-sensitive, free-format language
• Data items can be constants or variables

11
Data Types (continued)

• A declaration of a data item tells
• Whether the item is a constant or a variable
• The identifier used to name the item
• The data type of the item

12
Data Types (continued)

• Some of C standard data types
• int a positive or negative integer
• double a real number( double precision )
• float a real number ( single precision )
• char a character ( single keyboard character like
  t

13
Data Types(continued)

• Data Declarations
• double radius
• Allocates space for a type double data item
• Associates the name radius with this item
• Associates a set of valid operations with this
  item
• double circumference 34.5
• Same as above, plus?
• Gives it an initial value (initializes it)
• See sample programs

14
Data Types(continued)

• Data Declarations
• double radius, circumference, area
• Declares three separate data items of type
  double
• const double PI 3.1416
• Allocates space for type double data item
• Associates the name PI with this item
• Associates a set of valid operations with this
  item
• Initializes the item with the value 3.1416
• Cannot be changed. It is a constant.

15
Statement Types

• Input/output statement
• Input statement
• Collects a specific value from the user for a
  variable within the program
• Output statement
• Writes a message or the value of a program
  variable to the users screen or to a file

16
Statement Types (continued)

• Assignment statement
• Assigns a value to a program variable
• Control statement
• Directs the flow of control
• Can cause it to deviate from usual sequential flow

17
Input/Output Statements

• Example
• Pseudocode
• Get value for Radius
• C
• cin gtgt Radius
• cin input stream
• Code for extraction operator (gtgt) and the
  definition of the cin stream come from the
  iostream library and std namespace

18

• /
• circle01.cpp
• Gets the radius of a circle
• /
• include ltiostreamgt
• using stdcin
• using stdcout
• int main()
• double radius 0.0
• cout ltlt "Please enter the radius " ltlt '\n'
• cin gtgt radius
• return 0

• i/o example 1
• cout prompt user for data
• ltlt (insertion operator)
• cin store data in a variable
• gtgt (extraction operator)

19
Input/Output Statements (continued)

• Example
• Pseudocode
• Print the value of Circumference
• C
• cout ltlt Circumference
• cout output stream
• Code for the insertion operator (ltlt) and the
  definition of the cout stream come from the
  iostream library and std namespace

20

• /
• circle02.cpp
• Gets the radius of a circle
• /
• include ltiostreamgt
• using stdcin
• using stdcout
• int main()
• double radius 0.0
• cout ltlt "Please enter the radius " ltlt '\n'
• cin gtgt radius
• cout ltlt The radius you entered is ltlt radius

• i/o example 2
• cout prompt user for data
• ltlt (insertion operator)
• cin store data in a variable
• gtgt (extraction operator)
• cout output data entered

21
The Assignment Statement

• General form
• Pseudocode
• Set the value of variable to arithmetic
  expression
• C
• variable expression
• Expression on the right is evaluated
• The result is written into the memory location
  named on the left

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Expressions in C
An expression in C is a sequence of operators
and operands which adhere to the C syntax
rules. The operators are grouped according to an
order of precedence, and associativity
Operator Precedence Associativity
( ) 1 na
, - , , -- , ! ( unary ) 2 L-gtR (a, -a, a, --a, !a)R-gtL (a, a--)
, /, 3 L-gtR
, - 4 L-gtR
lt, gt, lt, gt 5 L-gtR
, ! 6 L-gtR
7 L-gtR
8 L-gtR
9 R-gtL
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Expressions in C

• Example 1 a b c d
• Example 2 a b c d e
• Example 3 a (b c) (d-e)
• Example 4 a b / c
• Example 5 a b c
• Example 6 a b c d
• Other , -, , /, ???

Assume b 5, c 3, d 4, e 2
24

• /
• circle03.cpp
• Gets the radius of a circle,
  calculatesits circumference and prints out the
  result
• /
• include ltiostreamgt
• using stdcin
• using stdcout
• int main()
• const double PI 3.14159
• double radius 0.0, circumference 0.0
• cout ltlt "Please enter the radius " ltlt '\n'
• cin gtgt radius
• circumference 2 PI radius
• cout ltlt The circumference is

• i/o example 3
• cout prompt user for data
• ltlt (insertion operator)
• cin store data in a variable
• gtgt (extraction operator)
• cout output data entered

25
Control Statements

• Types of control mechanisms
• Sequential
• Instructions are executed in order
• Conditional
• Choice of which instructions to execute next
  depends on some condition
• Looping
• Group of instructions may be executed many times

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Control Statements (continued)

• Default mode of execution sequential
• Conditional flow of control
• Evaluation of a Boolean condition (also called a
  Boolean expression)
• Which programming statement to execute next is
  decided based on the value of the Boolean
  condition (true or false)

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Control Statements (continued)

• Conditional flow of control (continued)
• if-else statement
• if (Boolean condition)
• S1
• else
• S2
• if variation of the if-else statement
• if (Boolean condition)
• S1

28

• Figure 8.12
• Conditional Flow of Control
• (If-Else)

29

• Figure 8.13
• If-Else with Empty Else

30
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31
Control Statements (continued)

• Looping (iteration)
• The loop body may be executed repeatedly based on
  the value of the Boolean condition
• while statement
• while (Boolean condition)
• S1

32

• Figure 8.14
• While Loop

33
Data Types Revisited

• How to declare a data item which is a group of
  integers, doubles, chars
• int Hits12 // web page hits
• Allocates space for group of 12 integers
• Associates the name Hits with this group of
  integers
• Associates a set of valid operations with Hits
• Each integer in Hits has its own name
• The first integer is Hits0 the last is Hits11

34
Data Types Revisited

• An array
• Groups together a collection of memory locations,
  all storing data of the same type

Figure 8.6 A 12-Element Array Hits
35
Data Types Revisited(continued)

• Declaring a group of arrays ( i.e. a table )
• double WaterReadings 2 3
• Allocates space for two arrays of three real
  numbers
• 6 total numbers
• Associates the name WaterReadings with this
  table
• Associates set of valid operations with this
  table
• Each element in WaterReadings has its own name
• The number at row 1, column 2 is
  WaterReadings12
• The number at row 0, column 0 is
  WaterReadings00

36
Data Types Revisited(continued)

• Initializing an array
• Int Hits12 3,6,7,22,25,12,34, 9, 3,17,15,2
• Int Hits 3,6,7,22,25,12,34, 9, 3,17,15,2
• Same as above
• Int Hits12 3,6,7,22
• Initializes first 4 as specified
• Last 12 get 0
• double WaterReadings 23 14.3, 15.2,
  16.4, 13.9, 14.2, 12.7
• int myValue23 0, 0 // ?

37
Intro to C

• Lets look at some programs using arrays

38
Putting the Pieces Together

• At this point, we can
• Perform input and output
• Assign values to variables
• Direct the flow of control using conditional
  statements or looping
• For a complete program, we need to
• Assemble the statements in the correct order
• Fill in the missing pieces

39
High-level Languages Revisited

• Expectations of a high-level language program
• Programmer can take a macroscopic view of tasks
  primitive operations can be larger
• Programs will be portable
• Code will be closer to standard English and use
  standard mathematical notation

40
High-level Languages Revisited

• Consider equation ax2 bx c 0
• The roots are x ( b ? sqrt(b2 4ac) ) / 2a
• Using a high level language we could write
• discrim bb 4ac
• root1 (-b sqrt(discrim)) / (2a)
• root2 (-b sqrt(discrim)) / (2a)
• This closely resembles the way we look at the
  problemmathematically

41
Virtual Data Storage

• Programs dealing with circles might deal with
• Circle as geometric shape
• Circular garden, pool, tile
• Properties of circle
• Circumference, radius, diameter, area
• Relationships among properties
• Circumference ? ? d ? ? 2 ? r
• Area ? ? r2

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Virtual Data Storage (continued)

• Possible Data Items For Circle Programs
• Radius, Circumference, Diameter, Area and PI
• To deal with actual problems what kind of data
  items should these be?
• Numbers with fractional parts ? double (in C)
• PI never changes ? const (in C)

43
Virtual Data Storage (continued)

• What if we want to deal with a group of things
  that are all the same kind?
• For Example a list numbers
• Monthly sales figures ( Jan thru Dec )
• Midterm exam grades ( 35 of them )
• Electoral college votes by state ( 50 of them )
• Website hits per month ( Jan thru Dec )
• We can declare a group of like data items.

44
Virtual Data Storage (continued)

• How to represent a table of the same kind of data
  items?

Site 1 Site 2 Site 3
FinalReading 14.3 15.2 16.4
InitialReading 13.9 14.2 12.7

• Group of arrays?

45
Virtual Data Storage (continued)
Assume these array declarations in C
int Hits1 12 int Hits2 12 0 int
Hits3 12 0,1,2,3 int Hits4 12
0,1,2,3,4,5,6,7,8,9,10,11 double
WaterReadings1 23 double WaterReadings2
23 0 double WaterReadings3 23
14.3,15.2,16.4 double WaterReadings4
23 14.3,15.2,16.4,13.9,14.2,12.7
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Virtual Data Storage (continued)

• Hits1 - elements 0 - 3
• -1219546216 134521764 -1073757288
  134514065
• Hits2 - elements 0 - 11
• 0 0 0 0 0 0 0 0
  0 0 0 0
• Hits3 - elements 0 - 11
• 0 1 2 3 0 0 0 0
  0 0 0 0
• Hits4 - elements 0 - 11
• 0 1 2 3 4 5 6 7
  8 9 10 11

47
Virtual Data Storage (continued)

• WaterReadings1
• 3.76654e-313 -5.74686e-42 -5.74962e-42
• -5.64181e-42 -3.24569e-42 4.94066e-324
• WaterReadings2
• 0 0 0
• 0 0 0
• WaterReadings3
• 14.3 15.2 16.4
• 0 0 0
• WaterReadings4
• 14.3 15.2 16.4
• 13.9 14.2 12.7

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Meeting Expectations

• C meets the four expectations for a high-level
  programming language
• Expectations
• Programmer need not manage details of the
  movement of data items within memory, nor pay any
  attention to where they are stored

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Meeting Expectations (continued)

• Expectations (continued)
• Programmer can take a macroscopic view of tasks,
  thinking at a higher level of problem-solving
• Programs written in high-level languages will be
  portable rather than machine-specific
• Programming statements in a high-level language
• Will be closer to standard English
• Will use standard mathematical notation

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Managing Complexity Divide and Conquer

• Divide and conquer
• To solve a problem, divide it into smaller pieces
• In a computer program
• Divide the code into modules (subprograms), each
  doing a part of the overall task
• Empower these modules to work together to solve
  the original problem

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Figure 8.20 A More Detailed Structure Chart

• Figure 8.19
• A Structure Chart

52
Using Functions

• Function
• A module of code in C
• Named using ordinary C identifiers
• Subtask functions optional
• The main function mandatory

53
Using Functions (continued)

• To invoke a subtask function, the main function
  gives
• Name of the function
• Argument list for the function
• Argument list list of identifiers for variables
  that concern that function
• Any function can have its own constant and
  variable declarations

54
Writing Functions

• A function header consists of
• Return indicator classifies a function as a void
  or a nonvoid function
• Function identifier
• Parameter list
• By default, arguments in C are passed by value

55

• Figure 8.24
• The Outline for a C Function

56

• Figure 8.29
• Some C Terminology

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Object-Oriented Programming

• Object-oriented programming (OOP)
• A program is a simulation of some part of the
  world that is the domain of interest
• Each object is an example drawn from a class of
  similar objects
• Key elements of OOP
• Encapsulation
• A class consists of its subtask modules and its
  properties
• Both are encapsulated in the class

58
Object-Oriented Programming (continued)

• Key elements of OOP (continued)
• Inheritance
• Once a class A of objects is defined, a class B
  of objects can be defined as a subclass of A
• Polymorphism
• One name, the name of the service to be
  performed, has several meanings, depending on the
  class of the object providing the service

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What Have We Gained?

• Two major advantages of OOP
• Software reuse
• A more natural world view

60
Graphical Programming Graphics Primitives

• Bitmapped display
• The screen is made up of thousands of pixels,
  laid out in a two-dimensional grid
• Frame buffer
• Memory that stores the actual screen image
• The terminal hardware displays on the screen the
  frame buffer value of every individual pixel

61

• Figure 8.34
• Pixel Numbering System in a Bitmapped Display

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Graphics Primitives (continued)

• Graphics library
• Software containing a collection of functions
  that control the setting and clearing of pixels
• Virtually all modern programming languages come
  with a graphics library

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The Big Picture Software Engineering

• Software life cycle
• Overall sequence of steps needed to complete a
  large-scale software project
• Implementation represents a relatively small part
  of the cycle

64

• Figure 8.37
• Steps in the Software Development Life Cycle

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Scaling Up

• Programs written by students
• No longer than a few hundred lines
• Real-world programs
• 2, 3, or 4 orders of magnitude larger
• Large-scale software development
• Extensive planning and design needed
• A team of programmers needed
• Software engineering

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The Software Life Cycle

• Each step in the software development life cycle
• Has a specific purpose and activities
• Should result in a written document
• The feasibility study
• Problem specification
• Program design

67
The Software Life Cycle (continued)

• Algorithm selection or development, and analysis
• Coding
• Debugging
• Testing, verification, and benchmarking
• Documentation
• Maintenance

68
Modern Environments

• Integrated Development Environment (IDE) speeds
  development by providing
• A text editor
• A file manager
• A compiler
• A linker and loader
• Tools for debugging

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Summary

• In a high-level language, the programmer
• Need not manage storage
• Can think about the problem at a higher level
• Can use more powerful and more natural-language-li
  ke program instructions
• Can write a much more portable program

70
Summary

• C is an object-oriented, high-level programming
  language
• if-else statement creates a conditional flow of
  control
• while loop can be used for iteration
• Software life cycle overall sequence of steps
  needed to complete a large-scale software project