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Computer Science: An OverviewTenth Edition

by J. Glenn Brookshear

Chapter 6:Programming Languages

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Chapter 6: Programming Languages

• 6.1 Historical Perspective• 6.2 Traditional Programming Concepts• 6.4 Language Implementation

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Figure 6.1 Generations of programming languages

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Second-generation:Assembly language

• A mnemonic system for representing machine instructions– Mnemonic names for op-codes– Identifiers: Descriptive names for memory

locations, chosen by the programmer

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Assembly Language Characteristics

• One-to-one correspondence between machine instructions and assembly instructions– Programmer must think like the machine

• Inherently machine-dependent• Converted to machine language by a

program called an assembler

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Program Example

Machine language

156C166D505630CEC000

Assembly language

LD R5, PriceLD R6, ShippingChargeADDI R0, R5 R6ST R0, TotalCostHLT

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Third Generation Language

• Uses high-level primitives– Similar to our pseudocode in Chapter 5

• Machine independent (mostly)• Examples: FORTRAN, COBOL• Each primitive corresponds to a sequence

of machine language instructions• Converted to machine language by a

program called a compiler

Turkish, German, English etc. are natural languages but programming languages are formal languages.

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Figure 6.2 The evolution of programming paradigms

Imperative (procedural) paradigm:Programming process is the development of a sequence of commands that, when followed, manipulate data to produce the desired result (i.e. find an algorithm to solve the problem).

Declarative paradigm: Asks programmer to describe the problem to be solved rather than an algorithm to be followed.

Programming (software development) paradigms: Alternative approaches to the programming (software development process) process.

Functional paradigm: A program is constructed by connecting smaller program units (i.e. predefined functions) so that each unit’s outputs are used as inputs to another unit in such a way that the desired overall input-to-output relationship is obtained.

Object-oriented paradigmSoftware system is a collection of units (called objects) each of which is capable of performing the actions that are related to itself and as well as requesting actions of other objects.

Agent-oriented paradigm (?)Autonomous, proactive and social objects (a.k.a. dynamic objects).

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Figure 6.3 A function for checkbook balancing constructed from simpler functionsIn LISP, (Find_diff (Find_sum (Old_balance Credits) Find_sum (Debits))

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Figure 6.4 The composition of a typical imperative program or program unit

Statement categories in imperative and object-oriented languages: Declarative statementsCustomized terminology that is used later in the program. E.g. Names of data items.

Imperative statementsDescription of steps in the underlying algorithms

CommentsStatements written into the code in any langugage in order to improve the human readability of the program.

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Data Types

• Integer: Whole numbers• Real (float): Numbers with fractions• Character: Symbols• Boolean: True/false

Variable: Descriptive names (rather than numeric addresses) that refer to main memory locations. Changing the values in such locations results in value changes for the variable.

Data type: Type of the associated variable. It encompasses both the manner in which the data item (named by its variable) is encoded and the operations that can be performed on that data (or in general the variable).

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Variable Declarations

float Length, Width;

int Price, Total, Tax;

char Symbol;

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Figure 6.5 A two-dimensional array with two rows and nine columns

Data structure: A conceptual arrangement of data.

Homogeneous array: A block of values of the same type such as one-dimensional list, two-dimensional list with rows and columns and higher dimensional tables.

Indices: Integer values that specify rows, columns etc. of the elements of a homogeneous array.

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Figure 6.6 The conceptual structure of the heterogeneous array Employee

Heterogeneous array: Block of data in which different elements can have different types.An example in C:

struct {char Name[25]; int Age; float SkillRating;} Employee;

Employee.Age = Employee.Age + 1;Employee.SkillRating = 72.5;

Declaration

part

Imperative

part

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Figure 6.7 The for loop structure and its representation in C++, C#, and Java

Comments: provide an easy understanding of program statements. They are explanatory statements inserted within program statements.

In C++, C# and Java,

/* This is a comment */// This is a comment