CSE:141 Introduction to Programming

Faculty of Computer Science, IBABS-I (Spring 2010)

Lecture 2

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Lesson Plan

• Introduction to computation• Languages• Program life cycle

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What is computation?

• Earlier computer were fixed program (Declarative)– E.g Calculator

• Now, stored program computers(Imperative)– E.g Computers

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Computer System

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Memory Addressing• The capacity (size) of memory is described in

terms of number of bytes.• RAM capacities in a typical computer range

from 512 MB (megabyte) to 3 GB (gigabyte).• RAM is volatile – data is lost when power is

turned off.• Computers don't understand the alphabet.

They only understand 0’s and 1’s. • So computers map each alphabet character

to a series of sixteen 0's and 1's. For example, the letter E is 00000000 01000101.

• And each of the eight-bit groupings is a byte.

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Address Memory Contents

…

50,000

50,001

50,002

50,003

50,004

50,005

…

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A Programming Language is . . .

• a language with strict grammatical rules, symbols, and special words used to construct a computer program

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Code is . . .

• The product of translating an algorithm into a programming language

• Instructions for a computer that are written in a programming language

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Languages

• High level vs Low level• General purpose vs Targeted• Interpreted vs Compiled• Synatx vs Semantics

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The high level vs low level

High-Level Language (HLL)– closest to natural language– words, numbers, and math

symbols– not directly understood by

hardware– “portable” source code

(hardware independent)– Java, C, C++, COBOL,

FORTRAN, BASIC, Lisp, Ada, etc.

Machine Language(lowest level)

– least natural language for humans, most natural language for hardware

– just 0s and 1s– directly understood by

hardware– not portable (hardware

dependent)

Programming Language Hierarchy

H ard w are

M ach in e L an g u ag e

A ssem b ly L an u ag e

H ig h -L eve l L an g u ag e (H L L )

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General purpose vs Targeted Languages

• A "general purpose programming language" theoretically should be usable in multiple domains, but not specialized for any of them.

• A Targeted/Specific purpose programming 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 (from source to object code) is not a separate user step– translation is “on-line,” i.e. at run time

Compiler,

Assembler, or

Interpreter

SourceCode

ObjectCode

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Synatx vs Semantics

• Semantics– Grammatical rules for assigning meaning to a

sentence. • Syntax

– Grammatical rules for specifying correct word order and inflectional structure in a sentence.

• Example– “Baby milk drinks“ not correct syntactically but

can extract meaning “Baby drinks milk”

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Programming Shortcut?

THINKINGCODE

TEST

PROBLEM-SOLVING PHASE

IMPLEMENTATION PHASE

Shortcut?

Algorithm

Code

Problem

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Programming Life Cycle

Problem-Solving Analysis and Specification General Solution ( Algorithm ) Verify

Implementation Concrete Solution ( Code ) Test

Maintenance Use Maintain

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Sample Problem

• A programmer needs an algorithm to determine an employee’s weekly wages

• How would the calculations be done by hand?

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One Employee’s Wages • During one week an employee works 52 hours at the hourly

pay rate $24.75• How much is the employee’s wages? • Assume a 40.0 hour normal work week• Assume an overtime pay rate factor of 1.5

40 x $ 24.75 = $ 990.00

12 x 1.5 x $ 24.75 = $ 445.50___________

$ 1435.50

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If hours is over 40.0, thenwages = (40.0 * payRate) + (hours - 40.0) * 1.5 *payRate

otherwise, wages = hours * payRate

RECALL EXAMPLE ( 40 x $ 24.75 ) + ( 12 x 1.5 x $ 24.75 ) = $1435.50

Weekly Wages, in General

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Employee’s Weekly Wages

Objects: Employee, pay rate, hours worked, wagesAlgorithm: 1. Get the employee’s hourly pay rate 2. Get the hours worked this week 3. Calculate this week’s regular wages 4. Calculate this week’s overtime wages (if any) 5. Add the regular wages to overtime wages (if any) to determine

total wages for the week