Computer Programming

Engr. Muniba Ashfaq

DCSE UET Peshawar

• Course Pre-Requisite

– Basic Computing & Programming

• Text Book

– Dietel & Dietel, C++ How to program.

• Reference Book

– Robert Lafore, Object Oriented Programming in C++

Grading Criteria

• Mid term 25%

• Final term 50%

• Sessional 25%

Contents of Week 1

• What is a Computer and what are computer languages

• Machine languages, Assembly languages and High level languages

• Translators: Compilers, Interpreter, Assembler • History of C and C++ • C++ Standard Library • Structured Programming • Basic of a Typical C++ Environment • Algorithms, Pseudocode

What is a Computer?

• Electronic device that receives, stores, retrieves and process information

• Device capable of performing computations and making logical decisions.

consist of: • Software

– Instructions to command computer to perform actions and make decisions. (Programs that run on computer).

• Hardware – Various devices comprising computer

• Keyboard, screen, mouse, disks, memory, CD-ROM, processing units, …

Computer languages

• Defines the rules under which programs are written to make use of computers

• Machine languages

• Assembly languages

• High level languages

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Computer Languages

• Machine language • Only language computer directly understands

• Defined by hardware design – Machine-dependent

• Generally consist of strings of numbers – Ultimately 0s and 1s

• Instruct computers to perform elementary operations – One at a time

• Cumbersome for humans

• Example: +1300042774

+1400593419

+1200274027

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Computer Languages

• Assembly language • English-like abbreviations representing elementary

computer operations

• Clearer to humans

• Incomprehensible to computers – Translator programs (assemblers)

» Convert to machine language

• Example: LOAD BASEPAY

ADD OVERPAY

STORE GROSSPAY

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Computer Languages

• High-level languages • Similar to everyday English, use common

mathematical notations

• Single statements accomplish substantial tasks – Assembly language requires many instructions to accomplish

simple tasks

• Translator programs (compilers) – Convert to machine language

• Interpreter programs – Directly execute high-level language programs

• Example: grossPay = basePay + overTimePay

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History of C and C++

• History of C – Evolved from two other programming languages

• BCPL and B

– Dennis Ritchie (Bell Laboratories) • Added data typing, other features

– Development language of UNIX – Hardware independent

• Portable programs

– 1989: ANSI standard – 1990: ANSI and ISO standard published

• ANSI/ISO 9899: 1990

C and C++

• C is a high level language designed to be,

– Much easier to understand than assembler

– As powerful

– As fast

– “Close to the machine”

– portable

Libraries and Modules

• Don’t want to rewrite code someone else has already written – Expensive – Might make mistakes – User gets confused – Need to share resources with other programs

• Compile each source file • Link with other compiled source files and libraries • Now can execute our program • C++ is easy, learning how to use the libraries is

harder!

C++ Standard Library

• C programs consist of pieces/modules called functions – A programmer can create his own functions

• Advantage: the programmer knows exactly how it works

• Disadvantage: time consuming

– Programmers will often use the C++ library functions • Use these as building blocks

– Avoid re-inventing the wheel • If a premade function exists, generally best to use it rather

than write your own

• Library functions carefully written, efficient, and portable

Structured Programming

– Disciplined approach to writing programs

– Clear, easy to test and debug and easy to modify

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Basics of a Typical C Program Development Environment

• Phases of C++ Programs:

1. Edit

2. Preprocess

3. Compile

4. Link

5. Load

6. Execute

Program is created in the editor and stored on disk.

Preprocessor program processes the code.

Loader puts program in memory.

CPU takes each instruction and executes it, possibly storing new data values as the program executes.

Compiler creates object code and stores it on disk.

Linker links the object code with the libraries

Loader

Primary Memory

Compiler

Editor

Preprocessor

Linker

Primary Memory

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Disk

Disk

Disk

CPU

Disk

Disk

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Basics of a Typical C++ Environment

• Input/output – cin

• Standard input stream

• Normally keyboard

– cout

• Standard output stream

• Normally computer screen

– cerr

• Standard error stream

• Display error messages