C程序设计基础 英文版 课件 Chapter 5 Arrays

Chapter5Arrays数组Outlines5.1OneDimensionalArrays一维数组5.2MultidimensionalArrays多维数组2ScalarVariablesversusAggregateVariablesSofar,theonlyvariableswe’veseenarescalar:capableofholdingasingledataitem.Calsosupportsaggregatevariables,whichcanstorecollectionsofvalues.TherearetwokindsofaggregatesinC:

arraysstructures35.1One-DimensionalArrays一维数组Arraysletusstoreasetofdata数据可用来存储一组数据Anarrayisadatastructurecontaininganumberofdatavalues,allofwhichhavethesametype.数组包含一组变量，这些变量类型相同Thesevalues,knownaselements,canbeindividuallyselectedbytheirpositionwithinthearray.这些变量叫做数组元素Theelementsofaone-dimensionalarrayaarearrangedoneafteranotherinasinglerow(orcolumn):一维数组所有元素在内存中连续排列，占据连续的内存空间45

int

a

[10]；

a[0]a[1]...a[9]ArraynameThenumberofelementsArrayDeclarationThetypeofthearray’selements

Thesevalues,knownaselements,canbeindividuallyselectedbytheirpositionwithinthearray.Position---indexTheelementsofaone-dimensionalarrayaarearrangedoneafteranotherinasinglerow(orcolumn)5.1One-DimensionalArraysArrayVariableDeclarationTodeclareanarray,wemustspecifythetypeofthearray’selementsandthenumberofelements:

inta[10];Thelengthofthearraycanbeany(integer)constantexpression.Usingamacrotodefinethelengthofanarrayisanexcellentpractice:可以用宏定义来声明数组长度

#defineN10 … inta[N];65.1One-DimensionalArraysArraySubscriptingHowtoaccessanarrayelement?Theelementsofanarrayoflengthnareindexedfrom0ton–1.Ifaisanarrayoflength10,itselementsaredesignatedbya[0],a[1],…,a[9]:75.1One-DimensionalArraysArraySubscriptingExpressionsoftheforma[i]arelvalues,sotheycanbeusedinthesamewayasordinaryvariables:数组元素可以像普通变量一样用 a[0]=1; printf("%d\n",a[5]); ++a[i];

/*thesubscriptcanbeanyintegerexpression*/85.1One-DimensionalArrays数组惯用循环ArraySubscriptingManyprogramscontainfor

loopswhosejobistoperformsomeoperationoneveryelementinanarray.ExamplesoftypicaloperationsonanarrayaoflengthN:惯用法

IDIOM

for(i=0;i<N;i++) a[i]=0;/*clearsa*/

for(i=0;i<N;i++) scanf("%d",&a[i]);/*readsdataintoa*/

for(i=0;i<N;i++) sum+=a[i];/*sumstheelementsofa*/9Classexercise24:reversethearrayProgram:ReversingaSeriesofNumbers逆序输出enteraseriesofnumbers,thenwritesthenumbersinreverseorder:

Enter10numbers:34824910279423115031 Inreverseorder:31501123947102498234Theprogramstoresthenumbersinanarrayasthey’reread,thengoesthroughthearraybackwards,printingtheelementsonebyone.10

#include<stdio.h>

#defineN10

intmain(){inta[N],i;

printf("Enter%dnumbers:",N);for(i=0;i<N;i++)scanf("%d",&a[i]);

printf("Inreverseorder:");for(i=N-1;i>=0;i--)printf("%d",a[i]);printf("\n");

return0;}115.1One-DimensionalArraysArraySubscriptingOutofArrayBounds下标越界Cdoesn’trequirethatsubscriptboundsbechecked;ifasubscriptgoesoutofrange,theprogram’sbehaviorisundefined.Acommonmistake:forgettingthatanarraywithnelementsisindexedfrom0ton–1,not1ton: inta[10],i;

for(i=1;i<=10;i++) a[i]=5;

Withsomecompilers,thisinnocent-lookingfor

statementcausesaninfiniteloop.125.1One-DimensionalArraysArraySubscriptingAnarraysubscriptmaybeany

integerexpression:

a[i+j*10]=0;Theexpressioncanevenhavesideeffects:

i=0; while(i<N) a[i++]=0;数组元素的下标可以用表达式表示135.1One-DimensionalArraysArrayInitialization数组初始化Themostcommonformofarrayinitializerisalistofconstantexpressionsenclosedinbracesandseparatedbycommas:

inta[10]={1,2,3,4,5,6,7,8,9,10};1412345678910a[0]a[1]a[2]a[3]a[4]a[5]a[6]a[7]a[8]a[9]5.1One-DimensionalArraysArrayInitialization初值少于数组长度，缺省的默认为0（整型实型数组）Iftheinitializerisshorterthanthearray,theremainingelementsofthearrayaregiventhevalue0:

intb[10]={1,2,3,4,5,6}; /*initialvalueofais{1,2,3,4,5,6,0,0,0,0}*/Usingthisfeature,wecaneasilyinitializeanarraytoallzeros:

intb[10]={0}; /*initialvalueofais{0,0,0,0,0,0,0,0,0,0}*/

There’sasingle0insidethebraces.155.1One-DimensionalArraysArrayInitializationIt’sillegalforaninitializertobecompletelyempty.It’salsoillegalforaninitializertobelongerthanthearrayitinitializes.Ifaninitializerispresent,thelengthofthearraymaybeomitted:

intb[]={1,2,3,4,5,6,7,8,9,10};Thecompilerusesthelengthoftheinitializertodeterminehowlongthearrayis.数组长度缺省，默认其长度等于初值的个数165.1One-DimensionalArraysDesignatedInitializers(C99)指定初始化It’softenthecasethatfewelementsofanarrayneedtobeinitializedexplicitly;theotherelementscanbegivendefaultvalues.{0forint,‘\0’forchar}Anexample:

intb[10]= {0,

0,

1,

0,

0,

2,

0,

0,

3,

0};C99’sdesignatedinitializerscanbeusedtosolvethisproblem.Here’showwecouldredothepreviousexampleusingadesignatedinitializer:

inta[15]={[2]=1,[5]=2,[8]=3};有时，用户只想对其中几个数组元素初始化，就用“指定初始化”,其他元素默认为0.175.1One-DimensionalArraysDesignatedInitializers(C99)Designatorsmustbeintegerconstantexpressions.Ifthelengthofthearrayisomitted,adesignatorcanbeanynonnegativeinteger.Thecompilerwilldeducethelengthofthearrayfromthelargestdesignator.数组长度缺省的时候，根据初值的标识符来推导其长度。Thefollowingarraywillhave24elements:

int

b[]

=

{[5]

=

10,

[23]

=

13,

[11]

=

36,

[15]

=

29};Aninitializermayuseboththeolder(element-by-element)techniqueandthenewer(designated)technique:可以同时用老的方法和新的方法来初始化：

inta[10]={9,

3,

2,

[4]

=

6,

1,

9,

[8]

=

8};189320619080a[0]a[1]a[2]a[3]a[4]a[5]a[6]a[7]a[8]a[9]5.1Variable-LengthArrays

inti,length;Scanf(“%d”,&length);//10

inta[length];

for(i=0;i<length;i++) if(i%2==0) a[i]=2; else a[i]=1;192121212121a[0]a[1]a[2]a[3]a[4]a[5]a[6]a[7]a[8]a[9]5.2MultidimensionalArraysAnarraymayhaveanynumberofdimensions.Thefollowingdeclarationcreatesatwo-dimensionalarray(amatrix,inmathematicalterminology):

intm[5][9];m

has5rowsand9columns.Bothrowsandcolumnsareindexedfrom0:20a[0][0]a[0][1]a[0][2]a[0][3]a[1][0]a[1][1]a[1][2]a[1][3]a[2][0]a[2][1]a[2][2]a[2][3]21e.g：inta[3][4];Column0123row0row1row2Toaccesstheelementofa

inrowi,columnj,wemustwritea[i][j].5.2MultidimensionalArraysAlthoughwevisualizetwo-dimensionalarraysastables,that’snotthewaythey’reactuallystoredincomputermemory.Cstoresarraysinrow-majororder,withrow0first,thenrow1,andsoon.Howthem[5][9]arrayisstored:22多维数组在内存中实际上是一维数组23

a[0][0]a[0][1]a[0][2]a[1][0]a[1][1]a[1][2]Theexpressionm[i]

designatesrowiofm,andm[i][j]thenselectselementjinthisrow.

a[0]---------a[0][0]a[0][1]a[0][2]a[2][3] a[1]---------a[1][0]a[1][1]a[1][2]在内存中，二维数组是按行排列的 。

a[0]即先存放a[0]行，再存放a[1]行。

a[1]5.2MultidimensionalArraysNestedforloopsareidealforprocessingmultidimensionalarrays.Considertheproblemofinitializinganarrayforuseasanidentitymatrix.Apairofnestedfor

loopsisperfect:

通常用两重循环（循环嵌套）来处理二维数组

for(row=0;row<N;row++) for(col=0;col<N;col++)

prinf(“%d”,a[row][col]);for(i=0;i<5;i++) for(j=0;j<5;j++)scanf(“%d”,&a[i][j]);24Variable-Length2DarrayDeclarenEnternDeclarethearrayEntertheelementsOutput25intn;scanf(“%d”,&n);inti,a[n][n];for(i=0;i<n;i++) for(j=0;j<n;j++)

scanf(“%d”,&a[i][j]);for(i=0;i<n;i++)

{for(j=0;j<n;j++)

prinf(“%d”,a[i][j]);

prinf(“\n”);

}Classexercise25:thematrixAsktheusertoinputatwodimensionalarray(NXN),thenoutputthematrix.

DeclarenEnternDeclarethearrayEntertheelements(forloop)Output26for(i=0;i<n;i++) for(j=0;j<n;j++)5.2Arraysdiagonal

introw,col,n;Scanf(“%d”,&n);5

doublea[n][n];

for(row=0;row<n;row++) for(col=0;col<n;col++) if(row==col) a[row][col]=1.0; else a[row][col]=0.0;27a[0][0]a[0][1]a[0][2]a[0][3]a[0][4]a[1][0]a[1][1]a[1][2]a[1][3]a[1][4]a[2][0]a[2][1]a[2][2]a[2][3]a[2][4]a[3][0]a[3][1]a[3][2]a[3][3]a[3][4]a[4][0]a[4][1]a[4][2]a[4][3]a[4][4]Classexercise26:themaindiagonalAsktheusertoinputatwodimensionalarray(NXN),thenoutputthemaindiagonalelements.

DeclarenEnternDeclarethearrayEntertheelements(forloop)Output28a[0][0]a[0][1]a[0][2]a[1][0]a[1][1]a[1][2]a[2][0]a[2][1]a[2][2]Column012row0row1row2for(i=0;i<n;i++) for(j=0;j<n;j++)Classexercise27:thesecondarydiagonalAsktheusertoinputatwodimensionalarray(NXN),thenoutputthesumofthesecondarydiagonalelements.DeclarenEnternDeclarethearrayEntertheelements(forloop)Output29a[0][0]a[0][1]a[0][2]a[1][0]a[1][1]a[1][2]a[2][0]a[2][1]a[2][2]Column012row0row1row2for(i=0;i<n;i++) for(j=0;j<n;j++)5.2MultidimensionalArraysInitializingaMultidimensionalArray二维数组初始化Wecancreateaninitializerforatwo-dimensionalarraybynestingone-dimensionalinitializers:

intm[5][9]={{1,1,1,1,1,0,1,1,1}, {0,1,0,1,0,1,0,1,0}, {0,1,0,1,1,0,0,1,0}, {1,1,0,1,0,0,0,1,0}, {1,1,0,1,0,0,1,1,1}};3031Wecanevenomittheinnerbraces:Oncethecompilerhasseenenoughvaluestofillonerow,itbeginsfillingthenext.分隔行的内部大括号可以省略inta[3][4]={{1,2,3,4},{5,6,7,8},{9,10,11,12}};Or：inta[3][4]={1,2,3,4,5,6,7,8,9,10,11,12};row0

row1

row

2a[0][0]a[0][1]a[0][2]a[0][3]

a[1][0]a[1][1]a[1][2]a[1][3]

a[2][0]a[2][1]a[2][2]a[2][3]1234567891011125.2MultidimensionalArraysInitializingaMultidimensionalArrayIfaninitializerisn’tlargeenoughtofillamultidimensionalarray,theremainingelementsaregiventhevalue0.Thefollowinginitializerfillsonlythefirstthreerowsofm;thelasttworowswillcontainzeros: intm[5][9]={{1,1,1,1,1,0,1,1,1}, {0,1,0,1,0,1,0,1,0}, {0,1,0,1,1,0,0,1,0}};初始化的时候如果只提供部分初值，则其他默认为0325.2MultidimensionalArraysInitializingaMultidimensionalArrayIfaninnerlistisn’tlongenoughtofillarow,theremainingelementsintherowareinitializedto0:

intm[5][9]={{1,1,1,1,1,0,1,1,1}, {0,1,0,1,0,1,0,1}, {0,1,0,1,1,0,0,1}, {1,1,0,1,0,0,0,1}, {1,1,0,1,0,0,1,1,1}};335.2MultidimensionalArraysInitializingaMultidimensionalArray指定初始化C99’sdesignatedinitia