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CodingCoding

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C O D I N GC O D I N G The coding activity starts when some form of designThe coding activity starts when some form of design

has been done and the specifications of the modules to behas been done and the specifications of the modules to bedeveloped are available.developed are available.

 Implementation starts either Top-Down or Bottom-upImplementation starts either Top-Down or Bottom-up

 There are certain process that developer does whileThere are certain process that developer does while

coding i.e.coding i.e.

An Incremental Coding ProcessAn Incremental Coding Processrite code for assigned module and perform unit testingrite code for assigned module and perform unit testing

Develop code incrementally to facilitate debuggingDevelop code incrementally to facilitate debugging

Test driven DevelopmentTest driven Development!ere programmer first writes the test scripts and then writes the code!ere programmer first writes the test scripts and then writes the code

to pass the test.to pass the test.

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Programming Principles andProgramming Principles and

GuidelinesGuidelinesCommon Coding ErrorsCommon Coding ErrorsMemory LeaksMemory Leaks

Freeing an already freed resourceFreeing an already freed resource

NULL DereferencingNULL Dereferencing

Lack of unique addressLack of unique address

ync!roni"a#ion Errorsync!roni"a#ion Errors

$rray inde% ou# of &ound$rray inde% ou# of &ound

$ri#!me#ic e%cep#ions$ri#!me#ic e%cep#ions

'u(er o)er*o+'u(er o)er*o+

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#ruc#ured Programming#ruc#ured Programming

elec#ion using if con#rolelec#ion using if con#rolI#era#ion using +!ileI#era#ion using +!ile

equencingequencing

Informa#ion ,idingInforma#ion ,idingome programming Prac#icesome programming Prac#icesCon#rol Cons#ruc#sCon#rol Cons#ruc#s

Go#o-sGo#o-sDa#a #ype .user de/ned0 in &uil#1Da#a #ype .user de/ned0 in &uil#1

Nes#ingNes#ing

Module si"e0 in#erfaceModule si"e0 in#erface

Programming PrinciplesProgramming Principles

2Guidelines2Guidelines

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Coding ProcessCoding Process$n incremen#al coding process$n incremen#al coding process

 3es# dri)en de)elopmen# 3es# dri)en de)elopmen#

Pair programmingPair programming

ource code con#rol and &uild &yource code con#rol and &uild &y

reposi#oryreposi#ory

4efac#oring .C!ange in in#ernal s#ruc#ure14efac#oring .C!ange in in#ernal s#ruc#ure14educed coupling4educed coupling

Increased co!esionIncreased co!esion

'e##er Open Close principle'e##er Open Close principle

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C!arac#eris#ics of CodingC!arac#eris#ics of Codingimplici#yimplici#y

easy #o unders#andeasy #o unders#and4eada&ili#y4eada&ili#y

simple codesimple code

Good Documen#a#ionGood Documen#a#ion

unders#anda&ili#y 2 main#aina&ili#yunders#anda&ili#y 2 main#aina&ili#y 3ranspor#a&ili#y 3ranspor#a&ili#y

#o di(eren# en)ironmen##o di(eren# en)ironmen#

Usa&ili#yUsa&ili#y

good in#erfacegood in#erface

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C " D I # $C " D I # $  Programming Practices:Programming Practices:  Concept of %tructured ProgrammingConcept of %tructured Programming  Information !idingInformation !iding  Programming %tyles&Programming %tyles&

 #ames' #ames'

Control Constructs'Control Constructs'

$o to'$o to'Info. !iding'Info. !iding'

(ser Defined Data Types '(ser Defined Data Types '

 #esting' #esting'

  )odule %i*e')odule %i*e')odule Interface')odule Interface'

Program +ayout'Program +ayout'

,obust ness.,obust ness.  Internal DocumentationInternal Documentation

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C O D I N GC O D I N G Internal DocumentationInternal Documentation

 Internal documentation of the Program is done by use of comments.Internal documentation of the Program is done by use of comments. Comments are the tetual statements that are meant for the program reader not forComments are the tetual statements that are meant for the program reader not for

the eecution of the Program.the eecution of the Program.

 Comments if properly written and ept consistent with the code' can be invaluableComments if properly written and ept consistent with the code' can be invaluable

during maintenance.during maintenance.

 Comment is not needed for every +"C /sComment is not needed for every +"C /s

 Comments should be provided for the bloc of code especially for the bloc whichComments should be provided for the bloc of code especially for the bloc which

is hard to follow.is hard to follow.

 C"))0#T% 1", A )"D(+0 A,0 "1T0# CA++0D A%C"))0#T% 1", A )"D(+0 A,0 "1T0# CA++0D A% PROLOGUE.PROLOGUE.

 Prologue contains following desirable properties&Prologue contains following desirable properties&

)odule 1unctionality)odule 1unctionality

Parameter and their purposesParameter and their purposes

Assumptions about the input/sAssumptions about the input/s

$lobal variable accessed and2or modified module.$lobal variable accessed and2or modified module.

 Prologues are useful only if they are ept consistent with the logic of the module.Prologues are useful only if they are ept consistent with the logic of the module.

If module is modified then P,"+"$(0 should also be modified.If module is modified then P,"+"$(0 should also be modified.

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C O D I N GC O D I N G 3erification3erification

  3erification of the output of Coding Phase is primarily3erification of the output of Coding Phase is primarilyintended for detecting the errors.intended for detecting the errors.

 $oal of verification to see the consistency of the code.$oal of verification to see the consistency of the code.

 Two methods for the verification of the Program&Two methods for the verification of the Program&  %tatic )ethod%tatic )ethod

 Dynamic )ethodDynamic )ethod

 Dynamic methods are applicable on some test data and findDynamic methods are applicable on some test data and findout some errors lie traditional testing mechanism.out some errors lie traditional testing mechanism.

  %tatic methods are conceptual eecution' here program are%tatic methods are conceptual eecution' here program are

not tested lie dynamic.not tested lie dynamic.  Types of error detected through static method can not beTypes of error detected through static method can not beidentified by dynamic methods.identified by dynamic methods.

 Testing and static methods are complementary of each other.Testing and static methods are complementary of each other.

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C O D I N GC O D I N G 3erification3erification

 After writing the code the code is to be verified before it isAfter writing the code the code is to be verified before it is

used by others.used by others.

 3erification does not mean proving correctness of program.3erification does not mean proving correctness of program.

  3arious techni4ues lie inspection' (nit testing 5 Program3arious techni4ues lie inspection' (nit testing 5 Program

checing for verification.checing for verification.

 Code InspectionCode Inspection $eneral Approach that can be applied for detecting defects.$eneral Approach that can be applied for detecting defects.

 It is done after successful compilation of code.It is done after successful compilation of code.

 Costly affair Costly affair 

 Basically used to reduce human effort and timeBasically used to reduce human effort and time

 other techni4ue is Code ,eadingother techni4ue is Code ,eading

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C O D I N GC O D I N G %tatic Analysis%tatic Analysis

  It is basically a Program Checing and can be doneIt is basically a Program Checing and can be donein 6 waysin 6 ways

  )odel Checing)odel Checing  !ere abstract model of Program will be verified!ere abstract model of Program will be verified

 Dynamic AnalysisDynamic Analysis  !ere Program is Instrumented and checed with some data!ere Program is Instrumented and checed with some data

  %tatic Analysis%tatic Analysis  Analysis of the Program by methodically analy*ing the Program tet isAnalysis of the Program by methodically analy*ing the Program tet is

called %Acalled %A

  It is performed mechanically by using tools.It is performed mechanically by using tools.

 During %tatic Analysis the Program itself is not eecuted but the tet isDuring %tatic Analysis the Program itself is not eecuted but the tet is

input to toolinput to tool

  Aim is to generate the potential errors in the code.Aim is to generate the potential errors in the code.

 1or this purpose we use %tatic Analy*er 1or this purpose we use %tatic Analy*er 

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Code 5alk#!roug!sCode 5alk#!roug!s

I# is informal code analysis #ec!niqueI# is informal code analysis #ec!niqueE)alua#ed &y #eam of re)ie+ersE)alua#ed &y #eam of re)ie+ers

I# is no# pro6ec# re)ie+ &u# is dep#!I# is no# pro6ec# re)ie+ &u# is dep#!

e%amina#ion7e%amina#ion7

 3eam for i# includes Pro6ec# Leader0 3eam 3eam for i# includes Pro6ec# Leader0 3eam

mem&ers and represen#a#i)e form 8$mem&ers and represen#a#i)e form 8$

group7group7

Discussion on disco)ery of errors no# on !o+Discussion on disco)ery of errors no# on !o+#o /% #!e errors7#o /% #!e errors7

5alk#!roug! impro)es 3eam communica#ion5alk#!roug! impro)es 3eam communica#ion

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Pro)ing Correc#nessPro)ing Correc#ness

$ny proof #ec!nique mus# &egin +i#! a formal$ny proof #ec!nique mus# &egin +i#! a formalspeci/ca#ion of #!e program7 No formal proof canspeci/ca#ion of #!e program7 No formal proof can

&e pro)ided if +!a# +e !a)e #o pro)e is no# s#a#ed&e pro)ided if +!a# +e !a)e #o pro)e is no# s#a#ed

informally in an imprecise manner7informally in an imprecise manner7

$ program usually does no# opera#e on ar&i#rary se#$ program usually does no# opera#e on ar&i#rary se#

of inpu#7 ,ence i# is no# su9cien# #o s#a#e #!e goalof inpu#7 ,ence i# is no# su9cien# #o s#a#e #!e goal

of program7of program7

 3!e asser#ion a&ou# #!e e%pec#ed /nal s#a#e of a 3!e asser#ion a&ou# #!e e%pec#ed /nal s#a#e of a

program is called #!e pos# condi#ion of #!e program0program is called #!e pos# condi#ion of #!e program0

and #!e asser#ion a&ou# #!e inpu# condi#ion is calledand #!e asser#ion a&ou# #!e inpu# condi#ion is called#!e pre:condi#ion of #!e program7#!e pre:condi#ion of #!e program7

Of#en de/ning #!e pre condi#ion for +!ic! #!e pos#Of#en de/ning #!e pre condi#ion for +!ic! #!e pos#

condi#ion +ill &e sa#is/ed is #!e goal of proof7condi#ion +ill &e sa#is/ed is #!e goal of proof7

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 3!e a%ioma#ic approac! 3!e a%ioma#ic approac!

$ll #!e proper#ies of a program can &e de#ermined$ll #!e proper#ies of a program can &e de#ermineds#a#ically from #!e #e%# of #!e program0 +i#!ou#s#a#ically from #!e #e%# of #!e program0 +i#!ou#

ac#ually e%ecu#ing i#7ac#ually e%ecu#ing i#7

In a%ioma#ic model of ,oar ;0 #!e goal is #oIn a%ioma#ic model of ,oar ;0 #!e goal is #o

#ake #!e program and cons#ruc# a sequence of#ake #!e program and cons#ruc# a sequence ofasser#ions and #!e rules and #!e a%ioms a&ou#asser#ions and #!e rules and #!e a%ioms a&ou#

#!e s#a#emen# and opera#ions in a program7#!e s#a#emen# and opera#ions in a program7

Using ,oar no#a#ion0 #!e &asic asser#ion a&ou# aUsing ,oar no#a#ion0 #!e &asic asser#ion a&ou# a

program is of #!e formprogram is of #!e form

P{S}QP{S}Q

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 3!e a%ioma#ic approac! 3!e a%ioma#ic approac!

$%iom of $ssignmen#$%iom of $ssignmen#

4ule of composi#ion4ule of composi#ion

4ule for $l#erna#e s#a#emen#4ule for $l#erna#e s#a#emen#4ule of consequence4ule of consequence

4ule of i#era#ion4ule of i#era#ion

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,oare,oare’’s me#!od for pro)ings me#!od for pro)ing

correc#ness of programscorrec#ness of programs,oare sugges#ed in ?@=@ an inference,oare sugges#ed in ?@=@ an inference

sys#em +i#! +!ic! +e can pro)e proper#iessys#em +i#! +!ic! +e can pro)e proper#ies

of programs7of programs7

$ unique form of proof rules0 called ,oare$ unique form of proof rules0 called ,oare#riplesA#riplesA

P B8 4P B8 4

+!ere+!ereP is a precondi#ionP is a precondi#ion

8 is a program or a program s#a#emen#8 is a program or a program s#a#emen#

4 pos# condi#ion74 pos# condi#ion7

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$ssignmen#s$ssignmen#s

D $%iom of assignmen#sD $%iom of assignmen#s

PP {x = f}{x = f} 44

+!ere+!ere

P is deri)ed from 4 &y replacing allP is deri)ed from 4 &y replacing all

occurrences of % +i#! f7occurrences of % +i#! f7

E%ampleAE%ampleA

y ? ?y ? ? {y = y+1}{y = y+1} y ?y ?

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Composi#ionComposi#ion

DJDJ Inference rule for composi#ionInference rule for composi#ion

PP {Q1}{Q1} 4?4?   4?4? {Q2}{Q2} 44

PP {Q1; Q2}{Q1; Q2} 44

E%ampleAE%ampleA

%?%? {y = x}{y = x} y?y? y?y? {z=y}{z=y} "?"?

%?%?{y=x; z=y}{y=x; z=y} "?"?

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I#era#ionI#era#ionConsider #!e s#a#emen#A +!ile ' do Consider #!e s#a#emen#A +!ile ' do

DK Inference rule for i#era#ionDK Inference rule for i#era#ion  PP '' {S}{S} PP

  PP {while B do S}{while B do S} AA''  PP

E%ampleE%ample

% ?% ? % % {x = x+1}{x = x+1} % ?% ?

%?%? {while (x < 5) x = x + 1}{while (x < 5) x = x + 1} %%    % ?% ?

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if:#!en:elseif:#!en:else

D if:#!en:else inference ruleD if:#!en:else inference rule

PP  ee {Q1}{Q1} 44  PP  ee {Q2}{Q2} 44

  PP {if e then Q1 ele Q2 !}{if e then Q1 ele Q2 !} 44

E%ampleE%ample

" "  % % {y "= #x + z}{y "= #x + z} yy   " "  %%   {y "= x + z}{y "= x + z} yy  

 " " {if (x

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No#es on ,oare:s#yle rulesNo#es on ,oare:s#yle rules

Pro)esPro)es par#ial correc#nesspar#ial correc#nessi7e70 meaningless +!en #!e programi7e70 meaningless +!en #!e program

does no# #ermina#e7does no# #ermina#e7

If in addi#ion +e pro)e #ermina#ion0If in addi#ion +e pro)e #ermina#ion0

#!en +e !a)e#!en +e !a)e #o#al correc#ness#o#al correc#ness77

8A suppose #!a# y in our8A suppose #!a# y in our

program7 Does i# c!ange #!e proof Qprogram7 Does i# c!ange #!e proof Q

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No#es on ,oare:s#yle rulesNo#es on ,oare:s#yle rules

,oare logic is,oare logic is soundsound in #!e sense #!a#in #!e sense #!a#

e)ery#!ing #!a# can &e pro)ed ise)ery#!ing #!a# can &e pro)ed is

correc#correc#

 3!ere e%is#s e%#ensions #o all popular 3!ere e%is#s e%#ensions #o all popular

cons#ruc#sAcons#ruc#sA

recursionrecursionarrays0 poin#ers0777arrays0 poin#ers0777

concurrency777concurrency777

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JJ

Formal $nalysisFormal $nalysis

4efers #o #ool:&ased me#!ods used #o4efers #o #ool:&ased me#!ods used #o

e%plore0 de&ug0 and )erify formale%plore0 de&ug0 and )erify formal

speci/ca#ionsspeci/ca#ions

Me#!odsMe#!ods 3!eorem pro)ing 3!eorem pro)ing

Proof c!eckingProof c!ecking

Model c!eckingModel c!ecking

$nima#ion and simula#ion$nima#ion and simula#ion

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 3!ank Rou 3!ank Rou