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Announcement,請登入討論區網頁依照第二次期中考及格與否，有不同作業。,Notes,請多寫程式，甚至故意把程式寫錯是很重要的,Pointer指標，指位器,變數有三個屬性：位址、值和資料型態Variablehas3properties:itsaddress,value,anddatatype,inta=5;,address,0 xFFEA,5,a,int*b;,address,k=0 x12;*k=100;Ans:指標的值必須是有意義的,1.指標指向其他變數,利用指標指向其他變數。Usepointerstostoretheaddressofothervariables.,inta=5;int*b;,address,b=malloc(3*sizeof(int);,0 xFFEE,0 xFFF1,*b=1;/b0=1;*(b+1)=2;/b1=2;*(b+2)=3;/b2=3;,Question,Whatiswrongwiththis?,int*b;b=malloc(3);/3bytes,*b=1;/b0=1;*(b+1)=2;/b1=2;*(b+2)=3;/b2=3;,3.指標指向陣列,陣列名稱為一個指標常數。Thenameofanarrayvariableisanconstantpointer,inta3;int*b;b=a;,*b=1;/b0=1;*(b+1)=2;/b1=2;*(b+2)=3;/b2=3;,address,a+;,Example,#include#includevoidmain(void)chars=IamanidiotIamanidiot;inti,j;char*ptr;i=0;while(1)ptr=s+i;for(j=0;j13;j+)printf(%c,*(ptr+j);i+;i=i%14;system(cls);,4.指標指向二維陣列,Pointerisassignedtoan2-darray,inta23;int*b;b=a;,*b=1;/a00=1;*(b+1)=2;/a01=2;*(b+2)=3;/a02=3;*(b+3)=4;/a10=4;,address,s=(char*)malloc(sizeof(char)*nrow*ncol);,for(i=0;inrow;i+)for(j=0;jncol;j+)*(s+i*ncol+j)=0;,i=0,j=0,i=0,j=1,i=0,j=ncol-1,s,for(i=0;inrow;i+)for(j=0;jncol;j+)*(s+i+j*nrow)=0;,i=0,j=0,i=1,j=0,i=1,j=0,s,i=1,j=0,i=nrow-1,j=0,s+1,s+1,Exercise:動態分配記憶體做轉置矩陣,Inmatrixtranspose,Ccode,Whyusepointers?,UsedynamicallyallocatedmemoryHighleveldatastructureEx.Linkedlist(資料結構會教)Passparametersinfunctions,Ex.sum,#includeintsum(inta,intb);voidmain(void)inta=2,b=3,s;s=sum(a,b);printf(sum=%dn,s);intsum(inta,intb)/functioncanonlyreturnonevaluebackreturn(a+b);,Ex.Sumanddivision,Howtore-writetheabovefunctiontoreturntheresultofsumanddivision?,Ccode,Arrayofpointers,Sincepointerisakindofvariable,wecandeclareanarrayofpointers,#includevoidmain(void)int*a3;printf(%pn,a0);,address,a=0 xFFEA,0 xFFEE,0 xFFF1,a0,a1,a2,typedef:自訂資料型態,typedef:defineanewdatatype,#includevoidmain(void)typedefint*INTPTR;INTPTRa3;printf(%pn,a0);,動態宣告指標陣列dynamicallyallocatearrayofpointers,address,a=0 xFFEA,0 xFFEE,0 xFFF1,a0,a1,a2,a=0 xFFEA,#include#includevoidmain(void)int*a;a=malloc(3*sizeof(int*);printf(%pn,a0);,動態宣告指標陣列dynamicallyallocatearrayofpointers,Ifyouarenotcomfortablewithdoublepointers,trythis,#include#includevoidmain(void)typedefint*INTPTR;INTPTR*a;a=malloc(3*sizeof(INTPTR);printf(%pn,a0);,Twowaystodynamicallyallocate2-darrays(2),char*s;s=(char*)malloc(sizeof(char*)*nrow);for(i=0;inrow;i+)si=(char*)malloc(sizeof(char)*ncol);sij=a;/*accessdata*/,nrow,nco