C#入门经典解题答案.docx

C#入门经典解题答案.docx

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C#入门经典解题答案

问题解答

Chapter1:

IntroducingC#

Noexercises.

Chapter2:

WritingaC#Program

Noexercises.

Chapter3:

VariablesandExpressions

Exercise1

Q.Inthefollowingcode,howwouldyourefertothenamegreatfromcodeinthenamespacefabulous?

namespacefabulous

{

//codeinfabulousnamespace

}

namespacesuper

{

namespacesmashing

{

//greatnamedefined

}

}

A.

super.smashing.great

Exercise2

Q.Whichofthefollowingisnotalegalvariablename?

a.myVariableIsGood

b.99Flake

c._floor

dtime2GetJiggyWidIt

e

A.

b.Becauseitstartswithanumber,and,

eBecauseitcontainsafullstop.

Exercise3

Q.Isthestring"supercalifragilisticexpialidocious"toobigtofitinastringvariable?

Why?

A.No,thereisnotheoreticallimittothesizeofastringthatmaybecontainedinastringvariable.

Exercise4

Q.Byconsideringoperatorprecedence,listthestepsinvolvedinthecomputationofthefollowingexpression:

resultVar+=var1*var2+var3%var4/var5;

A.The*and/operatorshavethehighestprecedencehere,followedby+,%,andfinally+=.Theprecedenceintheexercisecanbeillustratedusingparenthesesasfollows:

resultVar+=（（（var1*var2）+var3）%（var4/var5））;

Exercise5

Q.Writeaconsoleapplicationthatobtainsfourintvaluesfromtheuseranddisplaystheirproduct.

A.

staticvoidMain（string[]args）

{

intfirstNumber,secondNumber,thirdNumber,fourthNumber;

Console.WriteLine（"Givemeanumber:

"）;

firstNumber=Convert.ToInt32（Console.ReadLine（））;

Console.WriteLine（"Givemeanothernumber:

"）;

secondNumber=Convert.ToInt32（Console.ReadLine（））;

Console.WriteLine（"Givemeanothernumber:

"）;

thirdNumber=Convert.ToInt32（Console.ReadLine（））;

Console.WriteLine（"Givemeanothernumber:

"）;

fourthNumber=Convert.ToInt32（Console.ReadLine（））;

Console.WriteLine（"Theproductof{0},{1},{2},and{3}is{4}.",

firstNumber,secondNumber,thirdNumber,fourthNumber,

firstNumber*secondNumber*thirdNumber*fourthNumber）;

}

NotethatConvert.ToInt32（）isusedhere,whichisn’tcoveredinthechapter.

Chapter4:

FlowControl

Exercise1

Q.Ifyouhavetwointegersstoredinvariablesvar1andvar2,whatBooleantestcanyouperformtoseeifoneortheother（butnotboth）isgreaterthan10?

A.（var1>10）^（var2>10）

Exercise2

Q.WriteanapplicationthatincludesthelogicfromExercise1,obtainstwonumbersfromtheuser,anddisplaysthem,butrejectsanyinputwherebothnumbersaregreaterthan10andasksfortwonewnumbers.

A.

staticvoidMain（string[]args）

{

boolnumbersOK=false;

doublevar1,var2;

var1=0;

var2=0;

while（!

numbersOK）

{

Console.WriteLine（"Givemeanumber:

"）;

var1=Convert.ToDouble（Console.ReadLine（））;

Console.WriteLine（"Givemeanothernumber:

"）;

var2=Convert.ToDouble（Console.ReadLine（））;

if（（var1>10）^（var2>10））

{

numbersOK=true;

}

else

{

if（（var1<=10）&&（var2<=10））

{

numbersOK=true;

}

else

{

Console.WriteLine（"Onlyonenumbermaybegreaterthan10."）;

}

}

}

Console.WriteLine（"Youentered{0}and{1}.",var1,var2）;

}

Thiscanbeperformedbetterusingdifferentlogic,forexample:

staticvoidMain（string[]args）

{

boolnumbersOK=false;

doublevar1,var2;

var1=0;

var2=0;

while（!

numbersOK）

{

Console.WriteLine（"Givemeanumber:

"）;

var1=Convert.ToDouble（Console.ReadLine（））;

Console.WriteLine（"Givemeanothernumber:

"）;

var2=Convert.ToDouble（Console.ReadLine（））;

if（（var1>10）&&（var2>10））

{

Console.WriteLine（"Onlyonenumbermaybegreaterthan10."）;

}

else

{

numbersOK=true;

}

}

Console.WriteLine（"Youentered{0}and{1}.",var1,var2）;

}

Exercise3

Q.Whatiswrongwiththefollowingcode?

inti;

for（i=1;i<=10;i++）

{

if（（i%2）=0）

continue;

Console.WriteLine（i）;

}

A.Thecodeshouldread:

inti;

for（i=1;i<=10;i++）

{

if（（i%2）==0）

continue;

Console.WriteLine（i）;

}

Usingthe=assignmentoperatorinsteadoftheBoolean==operatorisacommonmistake.

Exercise4

Q.ModifytheMandelbrotsetapplicationtoreQuestimagelimitsfromtheuseranddisplaythechosensectionoftheimage.Thecurrentcodeoutputsasmanycharactersaswillfitonasinglelineofaconsoleapplication;considermakingeveryimagechosenfitinthesameamountofspacetomaximizetheviewablearea.

A.

staticvoidMain（string[]args）

{

doublerealCoord,imagCoord;

doublerealMax=1.77;

doublerealMin=-0.6;

doubleimagMax=-1.2;

doubleimagMin=1.2;

doublerealStep;

doubleimagStep;

doublerealTemp,imagTemp,realTemp2,arg;

intiterations;

while（true）

{

realStep=（realMax-realMin）/79;

imagStep=（imagMax-imagMin）/48;

for（imagCoord=imagMin;imagCoord>=imagMax;

imagCoord+=imagStep）

{

for（realCoord=realMin;realCoord<=realMax;

realCoord+=realStep）

{

iterations=0;

realTemp=realCoord;

imagTemp=imagCoord;

arg=（realCoord*realCoord）+（imagCoord*imagCoord）;

while（（arg<4）&&（iterations<40））

{

realTemp2=（realTemp*realTemp）-（imagTemp*imagTemp）

-realCoord;

imagTemp=（2*realTemp*imagTemp）-imagCoord;

realTemp=realTemp2;

arg=（realTemp*realTemp）+（imagTemp*imagTemp）;

iterations+=1;

}

switch（iterations%4）

{

case0:

Console.Write（"."）;

break;

case1:

Console.Write（"o"）;

break;

case2:

Console.Write（"O"）;

break;

case3:

Console.Write（"@"）;

break;

}

}

Console.Write（"\n"）;

}

Console.WriteLine（"Currentlimits:

"）;

Console.WriteLine（"realCoord:

from{0}to{1}",realMin,realMax）;

Console.WriteLine（"imagCoord:

from{0}to{1}",imagMin,imagMax）;

Console.WriteLine（"Enternewlimits:

"）;

Console.WriteLine（"realCoord:

from:

"）;

realMin=Convert.ToDouble（Console.ReadLine（））;

Console.WriteLine（"realCoord:

to:

"）;

realMax=Convert.ToDouble（Console.ReadLine（））;

Console.WriteLine（"imagCoord:

from:

"）;

imagMin=Convert.ToDouble（Console.ReadLine（））;

Console.WriteLine（"imagCoord:

to:

"）;

imagMax=Convert.ToDouble（Console.ReadLine（））;

}

}

Chapter5:

MoreAboutVariables

Exercise1

Q.Whichofthefollowingconversionscan’tbeperformedimplicitly:

a.inttoshort

b.shorttoint

c.booltostring

d.bytetofloat

A.Conversionsaandccan’tbeperformedimplicitly.

Exercise2

Q.Givethecodeforacolorenumerationbasedontheshorttypecontainingthecolorsoftherainbowplusblackandwhite.Canthisenumerationbebasedonthebytetype?

A.

enumcolor:

short

{

Red,Orange,Yellow,Green,Blue,Indigo,Violet,Black,White

}

Yes,becausethebytetypecanholdnumbersbetween0and255,sobyte-basedenumerationscanhold256entrieswithindividualvalues,ormoreifduplicatevaluesareusedforentries.

Exercise3

Q.ModifytheMandelbrotsetgeneratorexamplefromthelastchaptertousethefollowingstructforcomplexnumbers:

structimagNum

{

publicdoublereal,imag;

}

A.

staticvoidMain（string[]args）

{

imagNumcoord,temp;

doublerealTemp2,arg;

intiterations;

for（coord.imag=1.2;coord.imag>=-1.2;coord.imag-=0.05）

{

for（coord.real=-0.6;coord.real<=1.77;coord.real+=0.03）

{

iterations=0;

temp.real=coord.real;

temp.imag=coord.imag;

arg=（coord.real*coord.real）+（coord.imag*coord.imag）;

while（（arg<4）&&（iterations<40））

{

realTemp2=（temp.real*temp.real）-（temp.imag*temp.imag）

-coord.real;

temp.imag=（2*temp.real*temp.imag）-coord.imag;

temp.real=realTemp2;

arg=（temp.real*temp.real）+（temp.imag*temp.imag）;

iterations+=1;

}

switch（iterations%4）

{

case0:

Console.Write（"."）;

break;

case1:

Console.Write（"o"）;

break;

case2:

Console.Write（"O"）;

break;

case3:

Console.Write（"@"）;

break;

}

}

Console.Write（"\n"）;

}

}

Exercise4

Q.Willthefollowingcodecompile?

Why?

string[]blab=newstring[5]

string[5]=5thstring.

A.No,forthefollowingreasons:

*Endofstatementsemicolonsaremissing.

*2ndlineattemptstoaccessanon-existent6thelementofblab.

*2ndlineattemptstoassignastringthatisn’tenclosedindoublequotes.

Exercise5

Q.Writeaconsoleapplicationthatacceptsastringfromtheuserandoutputsastringwiththecharactersinreverseorder.

A.

staticvoidMain（string[]args）

{

Console.WriteLine（"Enterastring:

"）;

stringmyString=Console.ReadLine（）;

stringreversedString="";

for（intindex=myString.Length-1;index>=0;index--）

{

reversedString+=myString[index];

}

Console.WriteLine（"Reversed:

{0}",reversedString）;

}

Exercise6

Q.Writeaconsoleapplicationthatacceptsastringandreplacesalloccurrencesofthestringnowithyes.

A.

staticvoidMain（string[]args）

{

Console.WriteLine（"Enterastring:

"）;

stringmyString=Console.ReadLine（）;

myString=myString.Replace（"no","yes"）;

Console.WriteLine（"Replaced\"no\"with\"yes\":

{0}",myString）;

}

Exercise7

Q.WriteaconsoleapplicationthatplacesdoubleQuotesaroundeachwordinastring.

A.

staticvoidMain（string[]args）

{

Console.WriteLine（"Enterastring:

"）;

stringmyString=Console.ReadLine（）;

myString="\""+myString.Replace（"","\"\""）+"\"";

Console.WriteLine（"Addeddoublequotesareoundwords:

{0}",myString）;

}

OrusingString.Split（）:

staticvoidMain（string[]args）

{

Console.WriteLine（"Enterastring:

"）;

stringmyString=Console.ReadLine（）;

string[]myWords=myString.Split（''）;

Console.WriteLine（"Addingdoublequotesareoundwords:

"）;

foreach（stringmyWordinmyWords）

{

Console.Write（"\"{0}\"",myWord）;

}

}

Chapter6:

Functions

Exercise1

Q.Thefollowi