Chapter 8

Chapter 8

High-Level Programming Languages

2

Chapter Goals

• Describe the translation process and distinguish between assembly, compilation, interpretation, and execution

• Name four distinct programming paradigms and name a language characteristic of each

• Describe the following constructs: stream input and output, selection, looping, and subprograms

3

Chapter Goals

• Construct Boolean expressions and describe how they are used to alter the flow of control of an algorithm

• Define the concepts of a data type and strong typing

• Explain the concept of a parameter and distinguish between value and reference parameters

4

Chapter Goals

• Describe two composite data-structuring mechanisms

• Name, describe, and give examples of the three essential ingredients of an object-oriented language

5

Compilers

High-level language

A language that provides a richer (more English like) set of instructions

Compiler

A program that translates a high-level language program into machine code

6

Compilers

Figure 8.1 Compilation process

How does this differ fromthe assembly process?

7

Interpreters

Interpreter

A translating program that translates and executes the statements in sequence

– Assembler or compiler produce machine code as output, which is then executed in a separate step

– An interpreter translates a statement and then immediately executes the statement

– Interpreters can be viewed as simulators

8

Java

• Introduced in 1996 and became instantly popular

• Portability was of primary importance

• Java is compiled into a standard machine language called Bytecode

• A software interpreter called the JVM (Java Virtual Machine) takes the Bytecode program and executes it

9

Portability

PortabilityThe ability of a program to be run on different machines

Compiler portabilityA program in a standardized language can be compiled and run on any machine that has the appropriate compiler

Bytecode portabilityA program translated into Bytecode can be run on any machine that has a JVM

Do you understand the difference?

10

Portability

Figure 8.2 Portability provided by standardized languages versus interpretation by Bytecode

11

Portability

Figure 8.2 Portability provided by standardized languages versus interpretation by Bytecode

12

Programming Language Paradigms

Imperative or procedural model– Program describes the processing– FORTRAN, COBOL, BASIC, C, Pascal,

Ada, and C++

Functional model– Program is written terms of functions, return

an answer.– LISP, Scheme (a derivative of LISP), and ML

13


Logic model– Program consists of facts about objects and rules that

question the relationships among facts– PROLOG

Object-oriented model– Program consists of a set of objects and the

interactions among the objects– Smalltalk and Simula – C++ is as an imperative language with some object-

oriented features– Java is an object-oriented language with some

imperative features

14


We examine procedural and object-oriented languages in the rest of this chapter by looking at the functionality provided in these languages

We give examples in different languages to show how syntax used to provide the functionality

15

Functionality of Imperative Languages

Sequence

Executing statements in sequence until an instruction is encountered that changes this sequencing

Selection

Deciding which action to take

Iteration (looping)

Repeating an action

Do these concepts sound familiar?Let's review them.

16

Boolean Expressions

Boolean expression

A sequence of identifiers, separated by compatible operators, that evaluates to true or false

A Boolean expression can be

– A Boolean variable

– An arithmetic expression followed by a relational operator followed by an arithmetic expression

– A Boolean expression followed by a Boolean operator followed by a Boolean expression

17

Boolean Expressions

Variable

A location in memory that is referenced by an identifier that contains a data value

Thus, a Boolean variable is a location in memory that can contain either true or false

18

Boolean Expressions

Remember the relational operators?List them!

19

Strong Typing

Data type

A description of the set of values and the basic set of operations that can be applied to values of the type

Strong typing

The requirement that only a value of the proper type can be stored into a variable

vs. what?

20

Data Types

Integer numbers

Real numbers

Characters

Boolean values

Strings

21

Integers

What determines the range of an integer value?

Is the range of an integer value the same in all languages?

What operations can be applied to integers?

22

Reals

How are real values like integer values?

How do real values differ from integer values?

23

CharactersDo you remember

ASCII?

Extended ASCII?

UNICODE?

How many characters in Extended ASCII?

How many characters in UNICODE?

What does a relational operator between two characters mean?

Why are we discussing these again?

24

Boolean and Strings

What values can a Boolean variable be?

For what are Boolean expressions used?

What is a string?

What operations can be applied to strings?

25

Declarations

Declaration A statement that associates an identifier with a variable, an action, or some other entity within the language that can be given a name; the programmer can refer to that item by name

Reserved word A word in a language that has special meaning

Case-sensitive Uppercase and lowercase letters are considered the same

Declaration Example

27

Assignment statement

Assignment statement

An action statement (not a declaration) that says to evaluate the expression on the right-hand side of the symbol and store that value into the place named on the left-hand side

Named constant

A location in memory, referenced by an identifier, that contains a data value that cannot be changed

28

Input/Output Structures

Pseudocode algorithms used the expressions Read or Get and Write or Print

High-level languages view input data as a stream of characters divided into lines

Key to the processing

The data type determines how characters are to be converted to a bit pattern (input) and how a bit pattern is to be converted to characters (output)

29

Input/Output Structures

Read name, age, hourlyWage

name is a string; age is an integer; hourlyWage is a real

The data must be a string, an integer, and areal in that order.

30

Control Structures

Control structure

An instruction that determines the order in which other instructions in a program are executed

Can you name the ones we defined in the functionality of pseudocode?

31

Selection Statements

Figure 8.3 Flow of control of if statement

32

Selection Statements

The if statement allows the program to test the state of the program variables using a Boolean expression

33

Blocks

Notethe symbolsused toindicateblocksin eachlanguage

34

Cascading Ifs

If (temperature > 90)Write "Texas weather: wear shorts"

Else If (temperature > 50)Write "A little chilly: wear a light jacket"

Else If (temperature > 32)Write "Philadelphia weather: wear a heavy coat"

ElseWrite "Stay inside"

Why does this work correctly?

35

Looping Statements

Figure 8.4 Flow of control of while statement

36

Looping Statements

A count-controlled loop

Set sum to 0Set count to 1While (count <= limit)

Read numberSet sum to sum + numberIncrement count

Write "Sum is " + sum

Why is itcalled acount-controlledloop?

37

Looping Statements

38

Looping Statements

An event-controlled loop

Set sum to 0Set allPositive to trueWhile (allPositive)

Read numberIf (number > 0)

Set sum to sum + numberElse

Set allPositive to falseWrite "Sum is " + sum

Why is it called anevent-conrolledloop? What is theevent?

39

Subprogram Statements

We can give a section of code a name and use that name as a statement in another part of the program

When the name is encountered, the processing in the other part of the program halts while the named code is executed

40


What if the subprogram needs data from the calling unit?

Parameters

Identifiers listed in parentheses beside the subprogram declaration; sometimes called formal parameters

Arguments

Identifiers listed in parentheses on the subprogram call; sometimes called actual parameters

41


Figure 8.5 Subprogram flow of control

42


Figure 8.5 Subprogram flow of control

43


Value parameter

A parameter that expects a copy of its argument to be passed by the calling unit

Reference parameter

A parameter that expects the address of its argument to be passed by the calling unit

44


Think of arguments as being placed on a message board

45


46

Recursion

Recursion

The ability of a subprogram to call itself

Base case

The case to which we have an answer

General case

The case that expresses the solution in terms of a call to itself with a smaller version of the problem

47

Recursion

For example, the factorial of a number is defined as the number times the product of all the numbers between itself and 0:

N! = N * (N 1)!

Base case

Factorial(0) = 1 (0! is 1)

General Case

Factorial(N) = N * Factorial(N-1)

48

Asynchronous Processing

Asynchronous processing

Not synchronized with the program's action

– Clicking has become a major form of input to the computer

– Mouse clicking is not within the sequence of the program

– A user can click a mouse at any time during the execution of a program

49

Composite Data Types

Records

A named heterogeneous collection of items in which individual items are accessed by name

Arrays

A named homogeneous collection of items in which an individual item is accessed by its position (index) within the collection

50


Declare Record

51


Declare record variableUse record variable

52


Figure 8.8 Array variable tenThings accessed from 0..9

An Array

53


Declare Array

54


Access an Array

55

Functionality of Object-Oriented Languages

Remember the definitions from Chapter 6?

Encapsulate

Object class

Object in problem-solving phase

Object in implementation phase

Class in implementation phase

Instantiate

Don't worry!

We'll reviewthese concepts

56

Review

Object class (problem-solving phase)

A description of a group of objects with similar properties and behaviors

Object (problem-solving phase)

An entity or thing that is relevant in the context of a problem

Instantiate

Create an object from a class

57

Review

Encapsulation

A language feature that enforces information hiding (second definition)

Class (implementation phase)

A language construct that is a pattern for an object and provides a mechanism for encapsulating the properties and actions of the object class

Object (implementation phase)

An instance of a class

58

Review

Rememberthepattern?

Fromproblemto generaldescriptionto classdefinition toprogram

59

Inheritance and Polymorphism

Inheritance

A construct that fosters reuse by allowing an application to take an already-tested class and derive a class from it that inherits the properties the application needs

Polymorphism

The ability of a language to have duplicate method names in an inheritance hierarchy and to apply the method that is appropriate for the object to which the method is applied

60

Inheritance and Polymorphism

Inheritance and polymorphism work together

How?

They combine to allow the programmer to build useful hierarchies of classes that can be put into a library to be reused in different applications

61

Ethical Issues

Open-Source Software Development

What is open-source software?

What is proprietary software?

What are the arguments against

open-source software?

What are the arguments for open-

source software?

62

Who am I?

I am best known for structured programming.Can you defineit?I am also knownfor my wit. Canyou recall someof my witty sayings?

63

Do you know?

Was Bytecode the first interpreter for programcode?

What does the word "paradigm" mean? Howhas its meaning changed over time?

How many definitions can you think of for "bow"?

Documents

Chapter 8