IP02 Data Statements C

IntroductiontoProgramming(inC++)

Dataandstatements

Jordi Cortadella,Ricard Gavald,FernandoOrejasDept.LSI,UPC

Outline

Variables,datatypesandexpressions

Statements: Assignment Input/output Conditionalstatement

2Dept.LSI,UPCIntroductiontoProgramming

Variablesandliterals Variable: symbolicnametorepresentdatavalues. Avariableisusuallyassociatedwithamemorylocation.

Intuition:thinkofavariableasaboxcontainingvaluesofacertaintype.

InC++(andmanyotherlanguages),variablesmustbedeclaredbeforetheyareused.

Literal: aconstantofacertaintype. Examples:4,3.14159,4.1e8,true,"Greenland"

IntroductiontoProgramming Dept.LSI,UPC 3

3 trueint x bool z

Types Adatatypespecifies:

Thesetofvaluesthatdataofthattypecanhave Thetypeofoperationsthatcanbeperformedwiththedata.

Everyprogramminglanguagehasasetofbasicdatatypes.

BasicdatatypesinC++:int,double,bool,char,string,


Expressions Expression:acombinationofliterals,variables,operatorsandfunctionsthatisevaluatedandreturnsavalue

Examplesa+3(i 1)sqrt(x)log(4n)(i 3)

STATEMENTS


Statements Anyprogramminglanguagehasasetofbasicstatementstomanipulatedata(read,writeandtransform).

Aprogramconsistsofacombinationofdataandstatementstoperformsometask.

Aprogramcanbecomeanewstatement(function)thatcanbeusedinotherprograms.


Assignment Assignment isthefundamentalstatementofimperative languages:

variable =expression

Semantics: Thevalueoftheexpressionisevaluated Theresultisstoredinthevariable Thepreviousvalueofthevariableislost


AssignmentExamples

int x,i,j;...

//x=3,i=8,j=2

x=3i+j;//x=22,i=8,j=2

x=x i;

//x=14,i=8,j=2

j=0;

//x=14,i=8,j=0

Variableinitialization Variablescanbeinitialized

withanexpressionintheirdeclaration:

double pi=3.14159;double two_pi =2pi;stringmy_name ="Jordi";

Recommendation:declarethevariableswhenneeded(notbefore).Initializethevariableinthesamedeclarationwheneverpossible.


Sequenceofstatements Asequenceofstatements(notnecessarilyassignments)isexecutedsequentially:

statement_1;statement_2;...statement_n;


Example:swappingthevalueoftwovariables

Solution1

int x,y;

//Precondition:x=X,y=Yx=y;y=x;//Postcondition:x=Y,y=X

Whyisthissolutionincorrect?

Solution2

int x,y;

//Precondition:x=X,y=Yint z=x;x=y;y=z;//Postcondition:x=Y,y=X

Atemporaryvariableisrequired


?

Swappingtwointegerswithonlytwovariables

//Pre:x=A,y=B

x=x y;

//x=AB,y=B

y=x+y;

//x=AB,y=A

x=y x

//Post:x=B,y=A


BasicI/OinC++ cin andcout representtheprogramsdefaultinput andoutput devicesrespectively(usually,thekeyboardandthedisplay).

Simpleoperations:

//Readandstoreinavariablecin >>variable;//Writethevalueofanexpressioncout

ExamplesofI/OinC++#includeusingnamespacestd;...int x,y;double z;...cin >>x>>y>>z;cout

Divisionandremainder

//Input:readstwointegernumbers(a,b)//Output:writesthedivisionandremainder//ofa/b

int main(){int a,b;cin >>a>>b;cout

Revisitingtimedecomposition

//Input:readsanintegerN>=0thatrepresents//acertaintimeinseconds//Output:writesthedecompositionofNin//hours(h),minutes(m)andseconds(s)//suchthat0

Conditionalstatement

if (condition)statement1;else statement2;

condition isaBooleanexpression Semantics:iftheconditionevaluatestrue,

statement1 isexecuted,otherwisestatement2 isexecuted.


Conditionalstatement:example

int a,b,m;...//Calculationofthemaximumoftwonumbers//Pre:a=A,b=B

if (a>=b)m=a;else m=b;

//Post:a=A,b=B,m=max(A,B)


Theelse partisoptional

//Input:readsanintegernumber//Output:writestheabsolutevalue//ofthenumber

intmain(){int a;cin >>a;if (a

Minandmaxoftwonumbersint a,b,minimum,maximum;

//Pre:a=A,b=B//Post:a=A,b=B,//minimum=min(A,B),maximum=max(A,B)

if (a>=b){minimum=b;maximum=a;

}else {

minimum=a;maximum=b;

}


Blocksofstatementsareenclosedinside{}

Maxofthreenumbers(I)int a,b,c,m;

//Pre:a=A,b=B,c=C//Post:a=A,b=B,c=C,m=max(A,B,C)

if (a>=b){if (a>=c)m=a;else m=c;

}else {

if (b>=c)m=b;else m=c;

}


Maxofthreenumbers(II)

int a,b,c,m;


if (a>=band a>=c)m=a;elseif(b>=aand b>=c)m=b;else m=c;


Maxofthreenumbers(III)

int a,b,c,m;


if (a>=b)m=a;else m=b;//m=max(a,b)if (c>m)m=c;


IP02 Data Statements C

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