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Chapter-01

Introduction toComputers and C++ Programming

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Who are we?

Programmers

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What make us programmers?

People who write programs are called programmers.

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What is a Program?

A sequence of statements that instruct a computer in how to solve a problem is called a program.

Statment 1

Statment 2

Statment 3

. . .

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What is Programming?

• It is the process of planning a sequence of steps (called instructions) for a computer to follow.

STEP 1

STEP 2

STEP 3

. . .• The act of designing, writing and maintaining a program

is called programming.

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What kinds of statements do computers understand?

• A computer only understands machine language statements.

• A machine language statement is a sequence of ones and zeros that cause the computer to perform a particular action, such as add, subtract, multiply, …e.g,, Add two numbers 100000010

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Machine Language (ML)

ML statements are stored in a computer’s memory, which is a sequence of switches.

For convenience of representation,

an “on” switch is represented by 1, and

an “off” switch is represented by 0.

ML thus appears to be binary (base-2):

e.g, Add two numbers 100000010

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Lets see more about Computers

Chapter_01_2_Computer_Organization.ppt

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Back to Programming

Chapter_01_1_Programming_and_Languages.ppt

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Machine Language

• is not portable

• runs only on specific type of computer

• is made up of binary-coded instructions (strings of 0s and 1s)

• is the language that can be directly used by the

computer

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Early Computers

... required a programmer to write in machine language (ML) ...– Easy to make mistakes!– Such mistakes are hard to find!– Not portable -- only runs on one kind of

machine! (CPU)

Programming was very difficult!

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A Bright Idea

Devise a set of abbreviations (mnemonics) corresponding to the ML statements, plus a program to translate them into ML.

The abbreviations are an assembly language, and the program to translate them into machine language is called an assembler.

Assembler 100000010ADD

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Assembly Languages

Allowed a programmer to use mnemonics, which were more natural than binary numbers.+ Much easier to write programs+ Much easier to read programs+ Much easier to find and fix mistakes– Still not portable to different machines

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Assembly Language(middle level)

• a more or less human readable version of machine language

• words, abbreviations, letters and numbers replace 0s and 1s

• easily translated from human readable to machine executable code

• like machine code, not portable (hardware dependent)

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Devise a set of statements that are close to human language (if, while, do, ...),plus a program to translate them into ML.

The set of statements is called a high level language (HLL) and the program to translate them into machine language is called a compiler.

High Level Languages

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HLL Compilers

Where an assembler translates one mnemonic into one ML statement, a HLL compiler translates one HLL statement into multiple ML statements.

Compiler

10101100

00000000

00101110

00000000

00101110

00000000

z = x + y;

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HLLs

High level languages (like C++) are+ Much easier to write programs + Much easier to read programs+ Much easier to find and fix mistakes+ Portable from one machine to another

(so long as they keep to the language standard).

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High Level Languages

• are portable

• user writes program in language similar to natural language

• examples -- FORTRAN, COBOL, Pascal, Ada, Modula-2, C++, Java

• most are standardized by ISO/ANSI to provide an official description of the language

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High Level Languages

Language DescriptionBASIC Beginners All-purpose Symbolic Instruction Code.

A general programming language originallydesigned to be simple enough for beginners to learn.

FORTRAN Formula Translator. A language designed forprogramming complex mathematical algorithms.

COBOL Common Business-Oriented Language. A languagedesigned for business applications.

Pascal A structured, general purpose language designedprimarily for teaching programming.

C A structured, general purpose language developed atBell Labs. C offers both high-level and low-levelfeatures.

C++ Based on the C language, C++ offers object-orientedfeatures not found in C. Also invented at BellLaboratories.

Java An object-oriented language invented at SunMicrosystems. Java may be used to developprograms that run over the Internet, in a webbrowser.

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Interpreters

• Interpreters - another way to translate HLL to machine language or object code

– interpretation (from source to object code) is not a separate user step

– translation is “on-line,” i.e. at run time

Interpreter

High Level

Language

machine language

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Compilers vs. Assemblers vs. Interpreters

• Compilers and Assemblers– translation is a separate user step

– translation is “off-line,” i.e. not at run time

• Interpreters - another way to translate source to object code– interpretation is not a separate user step

– translation is “on-line,” i.e. at run time

AssemblerAssemblyLanguage

Machine Language

Compiler, or

Interpreter

High LevelLanguage

Machine Language

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Compilers vs. Interpreters

• Compiled programs execute faster than interpreted programs

• Interpreters are popular in program development environments in which programs are recompiled frequently as new features are added and errors are corrected.

Once a program is developed, a compiled version can be produced to run most efficiently.

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Where we use Interpreters?

• Java virtual machine

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Objectives in Programming

A program should solve a problem:+ correctly (it actually solves the problem)+ efficiently (without wasting time or space)+ readably (understandable by another person)+ in a user-friendly fashion

(in a way that is easy for its user to use).

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Running a Program

Program

Computer

Processing Data

Data input (input for the

program)

Data Output(Output of the

program)

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Running a Program

Data Output(output for the

program)

ProgramData Input

(input for the program)

Computer, Processing Data

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Summary

There are “levels” to computer languages:– ML consists of “low” level binary statements,

that is hard to read, write, and not portable.– Assembly uses “medium” level mnemonics:

easier to read/write, but not portable.– C++ is a “high” level language that is even

easier to read/write, and portable.