Chapter 8

High-Level Programming Languages

(modified by Erin Chambers)

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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

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Compilers

Figure 8.1 Compilation process

How does this differ from

the assembly process?

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Interpreters

Interpreter

A translating program that translates and executes the statements in sequence

Compilers 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

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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

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Portability

Portability

The ability of a program to be run on different machines

Compiler portability

A program in a standardized language can be compiled

and run on any machine that has the appropriate compiler

Bytecode portability

A program translated into Bytecode can be run on

any machine that has a JVM

Do you understand the difference?

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Portability

Figure 8.2
Portability provided by standardized languages versus interpretation by Bytecode

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Portability

Figure 8.2
Portability provided by standardized languages versus interpretation by Bytecode

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Programming Language Paradigms

Imperative or procedural model

Program executes a sequence of instructions to accomplish a task

FORTRAN, COBOL, BASIC, C, Pascal,
Ada, and C++

Functional model

Program is written terms of mathematical functions

LISP, Scheme (a derivative of LISP), and ML

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Programming Language Paradigms

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

Commonly used today because it allows clean interaction between different objects

Smalltalk, Python, Java and C++

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Programming Language Paradigms

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

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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

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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

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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

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Boolean Expressions

Example: Number1 < Number2

<=, >, >=, ==, !=

and, not, or, xor, nor, nand

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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

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Data Types

Integer numbers

Real numbers

Characters

Boolean values

Strings

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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?

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Reals

How are real values like integer values?

How do real values differ from integer values?

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Characters

Do 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?

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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?

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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

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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

Remember?

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Selection Statements

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

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Blocks

Note

the

symbols

used to

indicate

blocks

in each

language

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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"

Else

Write "Stay inside"

Why does this work correctly?

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Looping Statements

A count-controlled loop

Set sum to 0

Set count to 1

While (count <= limit)

Read number

Set sum to sum + number

Increment count

Write "Sum is " + sum

Why is it

called a

count-controlled

loop?

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Looping Statements

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Looping Statements

An event-controlled loop

Set sum to 0

Set allPositive to true

While (allPositive)

Read number

If (number > 0)

Set sum to sum + number

Else

Set allPositive to false

Write "Sum is " + sum

Why is it

called an

event-conrolled

loop?

What is the

event?

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2002-06-09T12:04:34