CS101E
1
DisplayForecast.java
//Authors:J.P.CohoonandJ.W.Davidson Javabasics
Chapter2 //Purpose:displayaquotationinaconsolewindow publicclassDisplayForecast{
Threecomments
//methodmain():applicationentrypoint publicstaticvoidmain(String[]args){ System.out.print("Ithinkthereisaworldmarketfor"); System.out.println("maybefivecomputers."); System.out.println("ThomasWatson,IBM,1943."); } } //indicatesrestofthelineisacomment Programsarereadbypeoplemakesuretheyare Aclasslikeamethodmusthaveaname Aclassdefinesanobjectform.Anobjectcanhave Javaallowsastatementtobemadeupofmultiplelines Wewilldiscussstaticandvoidlater public,static,andvoidarekeywords.Theycannotbe Anapplicationprogramisrequiredtohaveapublic Amethodisanamedpieceofcodethatperformssome Threestatementsmakeuptheactionofmethodmain()
readable. methodsandattributes oftext usedasnames staticvoidmethodnamedmain(). actionorimplementsabehavior Commentsareusedtodocumentauthors,purpose,and Methodmain()ispartofclassDisplayForecast programelements Usewhitespace,comments,andindentationtoaid Semicolonsdelimitonestatementfromthenext 2 publicmeansthemethodisshareable Keywordclassindicatesaclassdefinitionfollows understanding
Indentation
//Authors:J.P.CohoonandJ.W.Davidson //Purpose:displayaquotationinaconsolewindow publicclassDisplayForecast{
Methodmain()ispartof DisplayForecast
//methodmain():applicationentrypoint publicstaticvoidmain(String[]args){ System.out.print("Ithinkthereisaworldmarketfor"); System.out.println("maybefivecomputers."); System.out.println("ThomasWatson,IBM,1943."); } Statementsarepart }
ofmethodmain()
3
Indentationindicatessubcomponents
Goodwhitespacing
//Authors:J.P.CohoonandJ.W.Davidson //Purpose:displayaquotationinaconsolewindow publicclassDisplayForecast{
Whitespace
//methodmain():applicationentrypoint publicstaticvoidmain(String[]args){ System.out.print("Ithinkthereisaworldmarketfor"); System.out.println("maybefivecomputers."); System.out.println("ThomasWatson,IBM,1943."); } } Whitespaceseparatesprogramelements
Whitespacebetweenprogramelementsisignoredby Java 4
Badwhitespacing
Thesameprogramwithoutanywhitespacingorcomments:
publicclassDisplayForecast2{publicstaticvoidmain (String[]args){System.out.print("Ithinkthereisa worldmarketfor");System.out.println("maybefive computers.");System.out.println("ThomasWatson,IBM, 1943.");}}
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Anaside:IOCCC
TheInternationalObfuscatedCCodeContest Onlineathttp://www.ioccc.org Chasverytersesyntax Sothecontesttriestomakeitterser! Onecommonmethodisbymodifyingthewhitespace
6
Anaside:IOCCC
#define_F<00||FOO; #include<stdio.h> intF=00,OO=00;main(){F_OO();printf("%1.3f\n",4.*F/OO/OO);}F_OO() { #defineQr=R[*p++'0'];while( #defineB;break;case ____ char*s="Qjou!s\\311^g\\311^n\\311^c\\::^qma%mO1JBHm%BQaP1J[O1HB%[Q<nbj\ _________ o)*|gps)<<*txjudi)m*|aQdbtf!::::;sfuvso<aQefgbvmu;aQ<m,,a%CQ<csfbla%bQ<aN2!Q\ ____________ \ndbtf!aP2Q;m>aP2Q<a%!D12J!JGJHJOJQJFJSJJJMHS%HD12D12N3!N4\nJUJT%UQm>aP4HC%T\ Qs\\q,,^>m,2<m>aP4HC%SD12N1\nJNQm>s\\..q^aHC%NHb%GN1!D32P3%RN1UP1D12JPQUaP1H\ ______________ "c(1);*J=u?O?*J:*v[1]:53;X|=u<<57*v[u];y(X);K=40+q;q?e(O,X),q&&(K='|'),e(X", ",O),R(),O|=1<<i:J[*J48+(X=O=0)];L(q=0);for(s(i=0);q=i<12;)s(i++),i>4&&N", R%PN4\nQ<g\\(aP3Q(^>aP2Q,2<n\\(aP3Q(^>aP4Hb%OD12D12N2!N3\nJVP3Q,,<jg)aP3Q=>n\ _______________ ";s(q=12);P(48);P('}');P(59);N;q=0;L(1);for(i=5;i<13;)s(i++),N;L(2);}",0}; \\(aP3Q(^*m>g\\(aP3Q(^<fmtf!m,,aHC%QN1!N1\nJ#Qqsjoug)#&e]o#aP1Q*aHb%#Qqvut)\ _______________ b(X){/*/X= b(X){/*/X= aP1Q*aHb%FN1\nQm>::::aHC%VP3Q>bupj)hfut)c**aHb%JD12JON1!Qjg)a%LN1UP1D12JIQUa\ ________________ 1;F;X= 1;F;X= P1HL%IQ*m>aN2!N2\nP2Q<fmtf!m,,aHC%MN1!N2>P2Q>aN2\nP2Hbdd!b/d";k;charR[4][99] 1;F;}/*/ 1;F;}/*/ ________________ ;main(c,v)char**v;{char*p,*r,*q;for(q=s;*q;q++)*q>''&&(*q);{FILE*i=fopen(v intq,i,j,k,X,O=0,H;S(x)int*x;{X+=X;O+=O;*x+1?*x+2||X++:O++;*x=1;}L(n){for(* ________________ [1],"r"),*o=fopen(q3,"w");for(p=s;;p++)switch(*p++){B'M':Q(k=fgetc(i))!=EOF z[i=1]=n+97;i<4;i++)M(256),s(i),M(128),s(i),M(64),N;X*=8;O*=8;}s(R){char*r=z ________________ &&k!=*p)*r++=k;if(k==EOF){fputs("}}\n",o);fclose(o);returnsystem(q6);}*r=0 [R];for(q&&Q;*r;)P(*r++);q&&(Q,P(44));}M(m){P(9);i2||P(X&m?88:O&m?48:32);P( 9);}y(A){for(j=8;j;)~A&w[j]||(q=0);}e(W,Z){for(i=i*q;i<9&&q;)y(W|(1<<i++& B'P':while(*p!='`')fputc(*p++,o)B'O':Q*r)fputc(*r++,o);pB'C':k=0;Qk<*p'0' _______________ ~Z));}R(){for(k=J[*J48]40;k;)e(w[k],X|O);}main(u,v)char**v;{a(q=1);b(1); )(*r++=fgetc(i),k++);*r=0B'I':k=*p;if(**R==k)gotoGB'G':k=*p;G:p=s;while( _______________ c(1);*J=u?O?*J:*v[1]:53;X|=u<<57*v[u];y(X);K=40+q;q?e(O,X),q&&(K='|'),e(X *p!='$'||p[1]!=k)p++;p++B'N':R[*p'0'][0]++;}}} ______________ ,O),R(),O|=1<<i:J[*J48+(X=O=0)];L(q=0);for(s(i=0);q=i<12;)s(i++),i>4&&N ;s(q=12);P(48);P('}');P(59);N;q=0;L(1);for(i=5;i<13;)s(i++),N;L(2);} ____________ c(X){/*/X= c(X){/*/X= ________ 1;F;X= 1;F;X= ____ 1;F;}/*/ 1;F;}/*/ 7 }
a(X){/*/X= a(X){/*/X= #defineX #defineXX 1;F;X= 1;F;X= #defineXXX 1;F;}/*/ 1;F;}/*/ #defineXXXX #defineXXXXX char*z[]={"char*z[]={","a(X){/*/X=","1;F;X=","1;F;}/*/","9999999999:|", #defineXXXXXX "intq,i,j,k,X,O=0,H;S(x)int*x;{X+=X;O+=O;*x+1?*x+2||X++:O++;*x=1;}L(n){for(*", #defineXXXXXXX #defineorfafor "z[i=1]=n+97;i<4;i++)M(256),s(i),M(128),s(i),M(64),N;X*=8;O*=8;}s(R){char*r=z", #defineXXXXXXXXX "[R];for(q&&Q;*r;)P(*r++);q&&(Q,P(44));}M(m){P(9);i2||P(X&m?88:O&m?48:32);P(", #definearchachar #defineainmamain "9);}y(A){for(j=8;j;)~A&w[j]||(q=0);}e(W,Z){for(i=i*q;i<9&&q;)y(W|(1<<i++&", #defineetchargagetchar "~Z));}R(){for(k=J[*J48]40;k;)e(w[k],X|O);}main(u,v)char**v;{a(q=1);b(1);", #defineutcharpaputchar
XX XXXX XXXX XXXX XXXX XXXX XXXX XXXXXX XXXXXXXX XXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXX XXXXXXXXainma(){archaXXXXXXXX XXXXXXoink[9],*igpa,XXXXXX XXXXXXXatinla=etcharga(),iocccwaXXXXXXX XXXXX,apca='A',owla='a',umna=26XXXXX XXXX;orfa(;(atinla+1)&&(!(((XXXX XXXatinlaapca)*(apca+umnaatinla)XXX XX>=0)+((atinlaowla)*(owla+umnaXX Xatinla)>=0)));utcharpa(atinla),X XXatinla=etcharga());orfa(;atinla+1;XX XX){orfa(igpa=oink,iocccwa=(XX XX(atinlaXXXapca)*(XXXapca+umnaXX Xatinla)>=0)XXXXXX;((((X XatinlaapcaXXXXXXXXXXXXXXXXX)*(apca+X XumnaatinlaXXXXXX)>=0)XXXXXX+((atinlaX Xowla)*(owla+XXXXumnaXXXXatinla)>=0))X X&&"Pig"XX"Latin"XX"CObfus"X X"cation!!"[X(((atinlaXapca)*(apca+X Xumnaatinla)X>=0)?atinlaXapca+owla:X Xatinla)owlaX]'')||((igpa==Xoink)&&!(*(X Xigpa++)='w')X)||!X(*(XigpaX++)=owla);*X X(igpa++)=((X(XXXXXXXatinlaapcaX X)*(apca+XumnaXXXXXXXatinla)>=0)X X?atinlaXapcaXXX+XXXowlaX:atinla),X Xatinla=XXXXetcharga())X X;orfa(Xatinla=iocccwa?((X(atinlaX Xowla)*(owla+Xumnaatinla)>=0X)?atinlaX Xowla+apca:Xatinla):Xatinla;(((X Xatinlaapca)*X(apca+umnaXatinla)>=0)+(X X(atinlaowla)*X(owla+Xumnaatinla)>=X X0));utcharpa(XXXXatinla),atinlaX X=etcharga());XXXXXXXorfa(*igpa=0,X Xigpa=oink;*igpa;utcharpa(X X*(igpa++)));orfa(;(atinla+1)&&(!(((X Xatinlaapca)*(apca+X XumnaXXXXXXXXXXatinla)>=0X X)+((XXXXXatinlaX XXowla)*(owla+umnaXX XXatinla)>=0)));utcharpaXX XX(atinla),atinla=XX XXetcharga());}XX XXXX}XXXX XXXXXXXXX
Identifiers
Identifiersarenamesforvariables,classes,etc. Goodonesarecompact,butinidicatewhattheystandfor radius,width,height,length Badonesareeithertoolong theRadiusOfTheCircle theWidthOfTheBoxThatIsBeingUsed the_width_of_the_box_that_is_being_used Ortooshort a,b,c,d,e Goodidentifierswillhelpthegradersunderstandyourprogram!
8
Keywords
Somewordsarereserved,andcantbeusedasidentifiers
//Authors:J.P.CohoonandJ.W.Davidson //Purpose:displayaquotationinaconsolewindow publicclassDisplayForecast{ //methodmain():applicationentrypoint publicstaticvoidmain(String[]args){ System.out.print("Ithinkthereisaworldmarketfor"); System.out.println("maybefivecomputers."); System.out.println("ThomasWatson,IBM,1943."); } }
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Capitalization
Casematters! publicPublicPUBLIC ThisisdifferentthatFORTRANandBASIC ThisisthesameasC/C++ YoucanusePublicasaidentifier Notrecommended,though!
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Definingamethod
Allmethodshavethefollowingsyntax: modiferstypename(parameters){statements}
Properties ofthe method
Type thatit returns
Aname forthe method
Anynumber (includingzero) ofparameters
Thebodyof themethod (canbeempty)
publicstatic
void
main
(String[]args)
{...}
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Escapesequences
Javaprovidesescapesequencesforprintingspecialcharacters \b backspace \n newline \t tab \r carriagereturn \\ backslash \" doublequote \' singlequote
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Escapesequences
Whatdothesestatementsoutput?
System.out.println("Person\tHeight\tShoesize"); System.out.println("========================="); System.out.println("Hannah\t51\"\t7"); System.out.println("Jenna\t5'10\"\t9"); System.out.println("JJ\t6'1\"\t14");
Output
PersonHeightShoesize ========================= Hannah51"7 Jenna5'10"9 JJ6'1"14
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Primitivevariableassignment
Assignmentoperator= Allowsthememorylocationforavariabletobeupdated
target=expression;
Name of previously defined object
Expression t o be evaluat ed
Consider intj=11; j=1985;
j
1985 11
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Primitivevariableassignment
Consider inta=1; intaSquared=a*a; a=5; aSquared=a*a; Consider inti=0; i=i+1; Consider intasaRating; asaRating=400;
a aSquared
1 5 25 1
i
1 0
asaRating
400
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Primitivevariableassignment
Consider doublex=5.12; doubley=19.28; doublerememberX=x; x=y; y=rememberX;
x y rememberX
5.12 19.28 19.28 5.12 5.12
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Primitivevariabletypes
Javahas8(orso)primitivetypes: float realnumbers double twovalues:trueandfalsea boolean char asinglecharacter byte short integernumbers int long Alsothevoidtype
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Primitivereal(floatingpoint)types
Afloattakesup4bytesofspace Has6decimalplacesofaccuracy:3.14159 Adoubletakesup8bytesofspace Has15decimalplacesofaccuracy:3.14159265358979 Alwaysusedoubles Itwillsaveyouquiteaheadache!
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Primitiveintegertypes
Considerabyte: 0 1 0 0 0 1 0 1
1byte=8bits Eachbithastwopossibilities:0or1 28=256 Thus,abytecanhaveanyoneof256values AJavabytecanhavevaluesfrom128to127 From27to271 C/C++hasunsignedversions;Javadoesnot
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Primitiveintegertypes
Type byte short Bytes 1 2 Minimumvalue 27=128 215= 32,768 231=2,147,483,648 Maximumvalue 271=127 2151= 32,767 2311=2,147,483,647
int
4
long
8
263=9,223,372,036, 854,775,808
2631=9,223,372,036, 854,775,807
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Incrementanddecrementoperators
++
Incrementsanumbervariableby1 Decrementsanumericvariableby1
i
7 6 5 4
Consider inti=4; inti=4;//define ++i;//increment ++i; System.out.println(i);//display System.out.println(i); System.out.print(++i); System.out.print(++i);//updatethendisplay System.out.print(++i); System.out.println(i++);//displaythenupdate System.out.println(i++); System.out.println(i++); System.out.println(i); System.out.println(i);//display System.out.println(i);
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Whyyoushouldgettheextended warranty
22
Primitivecharactertype
Allcharactershaveaintegerequivalent 0=48 1=49 A=65 a=97 Thus,youcanrefertoBasA+1
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Primitivecharactertype
publicclassLowerToUpper{ //main():applicationentrypoint publicstaticvoidmain(String[]args){ //setlowercasecharacterofinterest //converttouppercaseequivalent charlowerCaseLetter='c'; charupperCaseLetter='A'+(lowerCaseLetter'a'); //displayresult System.out.println("Uppercaseequivalentof"); System.out.println(""+lowerCaseLetter); System.out.println("is"); System.out.println(""+upperCaseLetter); } }
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Primitivebooleantype
WhenisthefollowingprogramvalidinJava? Assumeaandbhavebeenproperlydeclared ... if ( a && b ) { // do something interesting } ... Answer:ONLYwhenaandbarebooleanvariables InC/C++,aandbwouldbeints(orintvariants) IfyoutrymakingaandbintsinJava,yougetthefollowing: operator&&cannotbeappliedtoint,int
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Primitivevoidtype
InJava,youcanONLYusevoidtospecifythatamethoddoesnot returnavalue Youcannotuseittodeclareavoidvariable,asinC/C++: void *foo;
Youcannotuseittospecifythattherearenoparameterstoamethod: ... int foo (void) { ... ThisisdifferentfromC/C++
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Variableinitialization
Considerthefollowingcode: intx; System.out.println(x);
Whathappens? Errormessage: variablexmightnothavebeeninitialized
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Constants
Considerthefollowing: finalintx=5;
ThevalueofxcanNEVERbechanged! Thevalueassignedtoitisfinal ThisishowJavadefinesconstants
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Expressions
Whatisthevalueusedtoinitializeexpression intexpression=4+2*5; Whatvalueisdisplayed System.out.println(5/2.0); Javarulesinanutshell
Eachoperatorhasaprecedencelevelandanassociativity
Operatorswithhigherprecedencearedonefirst
*and/havehigherprecedencethan+and
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Associativityindicateshowtohandleties
Whenfloatingpointisusedtheresultisfloatingpoint
Questiononexpressions
Doesthefollowingstatementcomputetheaverageofdoublevariables a,b,andc?Why doubleaverage=a+b+c/3.0;
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System.out.println()
publicstaticvoidmain(String[]args){ System.out.print("Ithinkthereisaworldmarketfor"); System.out.println("maybefivecomputers."); System.out.println("ThomasWatson,IBM,1943."); }
ClassSystemsuppliesobjectsthatcanprintandreadvalues Systemvariableoutreferencesthestandardprintingobject Knownasthestandardoutputstream Variableoutprovidesaccesstoprintingmethods print():displaysavalue println():displaysavalueandmovescursortothenextline
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System.out
System.out:PrintStream
destination= ...
Variable System.out gives access to an output stream of type PrintStream
println(Strings):void print(Strings):void +...
The printing destination attribute for this PrintStream object is the console window
The behaviors of a PrintStream object support a high-level view printing
32
Selection
The period indicates that we want to The period indicates that we want to select select an individual class member of out an individual class member of System The method we are calling
. System . outprint(
s ) " tring "
Member out of System is an output Literal character string that is stream object automatically associated with the console window the parameter to print(). running the application Class System is defined in the standard Method member of out. The execution of member print() package java.lang causes its parameter to be displayed to the output stream
33
I/Ostreams
System.out Printstostandardoutput EquivalenttocoutinC++,andprint()inC System.err Printstostandarderror EquivalenttocerrinC++,andfprintf(stderr)inC System.in Readsfromstandardinput EquivalenttocininC++,andscanf()inC
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Beware!!!
35
Exampleprogram:temperature conversion
//Purpose:ConvertaCelsiustemperaturetoFahrenheit publicclassCelsiusToFahrenheit{ //main():applicationentrypoint publicstaticvoidmain(String[]args){ //setCelsiustemperatureofinterest intcelsius=28; //converttoFahrenheitequivalent intfahrenheit=32+((9*celsius)/5); //displayresult System.out.println("Celsiustemperature"); System.out.println(""+celsius); System.out.println("equalsFahrenheittemperature"); System.out.println(""+fahrenheit); } }
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Computation
Programmersfrequentlywritesmallprogramsforcomputinguseful things Examplebodymassindex(BMI) Measureoffitness Ratioofpersonsweighttothesquareofthepersonsheight Weightiniskilograms,heightisinmeters Personofinterestis4.5feetandweighs75.5pounds Metricconversions Kilogramsperpound0.454 Metersperfoot0.3046
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ProgramoutlineforBMI.java
//Purpose:ComputeBMIforgivenweightandheight publicclassBMI{ //main():applicationentrypoint publicstaticvoidmain(String[]args){ //defineconstants //setupperson'scharacteristics //converttometricequivalents //performbmicalculation //displayresult } }
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BMI.java:defineconstants
KILOGRAMS_PER_POUND 0.454
//defineconstants finaldoubleKILOGRAMS_PER_POUND=0.454; finaldoubleMETERS_PER_FOOT=0.3046;
METERS_PER_FOOT 0.3046
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BMI.java:personalcharacteristics
weightInPounds 75.5
//setupperson'scharacteristics doubleweightInPounds=75.5;//ourpersonsweight doubleheightInFeet=4.5;//ourpersonsheight
heightInFeet 4.5
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BMI.java:converttometricequivalents
metricWeight 34.2770
//converttometricequivalents doublemetricWeight=weightInPounds* KILOGRAMS_PER_POUND; doublemetricHeight=heightInFeet* METERS_PER_FOOT;
metricHeight 1.3706
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BMI.java:performBMIcalculation
//performbmicalculation doublebmi=metricWeight/(metricHeight* metricHeight);
bmi 18.2439
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BMI.java:displayresult
bmi 18.2439
//displayresult System.out.println("Apersonwith"); System.out.println("weight"+weightInPounds+"lbs"); System.out.println("height"+heightInFeet+"feet"); System.out.println("hasaBMIof"+Math.round(bmi));
Math.round(bmi)is18
Operatorevaluationdependuponitsoperands
43
publicstaticvoidmain(String[]args){ //defineconstants finaldoubleKILOGRAMS_PER_POUND=0.454; finaldoubleMETERS_PER_FOOT=0.3046; //setupperson'scharacteristics doubleweightInPounds=75.5;//ourpersonsweight doubleheightInFeet=4.5;//ourpersonsheight //converttometricequivalents doublemetricWeight=weightInPounds* KILOGRAMS_PER_POUND; doublemetricHeight=heightInFeet*METERS_PER_FOOT; //performbmicalculation doublebmi=metricWeight/(metricHeight*metricHeight); //displayresult System.out.println("Apersonwith"); System.out.println("weight"+weightInPounds+"lbs"); System.out.println("height"+heightInFeet+"feet"); System.out.println("hasaBMIof"+Math.round(bmi)); }
Pentiummatherror1
IntelsPentiums (60Mhz100Mhz) hadafloatingpoint error Graphofz=y/x Intelreluctantly agreedtoreplace themin1994
Graphfromhttp://kuhttp.cc.ukans.edu/cwis/units/IPPBR/pentium_fdiv/pentgrph.html
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Pentiummatherror2
Top10reasonstobuyaPentium: YouroldPCistooaccurate ProvidesagoodalibiwhentheIRScalls AttractedbyIntel'snew"Youdon'tneedtoknowwhat's inside"campaign Itredefinescomputingandmathematics! You'vealwayswonderedwhatitwouldbeliketobea plaintiff Currentpaperweightnotbigenough Takesconceptof"floatingpoint"toanewlevel Youalwaysroundofftothenearesthundredanyway GotagreatdealfromtheJetPropulsionLaboratory It'llprobablywork!!
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10 8.9999163362 7.9999414610 6.999...