Address 0000 0001 0002 0003 0004 0005 0006

โครงสรางของหนวยความจำ ทอยของขอ มล )Address) 0000 0001 0002 0003 0004 0005 0006 … Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ 15 ประเภท ชอตว แปร ขนาด int count 2 bytes 3. 1415 float pi 4 bytes 'A' char ch 1 bytes … … … XXXX ขอมล 01001012 Principle of Computer Programming 3 King Mongkut's Institute of Technology

ตวช (Pointers) ทอยของขอ มล )Address) 0000 0001 0002 0003 0004 0005 0006 … Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ ขอมล 15 ประเภท ชอตว แปร ขนาด int count 2 bytes 3. 1415 float pi 4 bytes 'A' char ch 1 bytes … … … XXXX 01001012 Principle of Computer Programming 0000 ptr = &count ตวช ptr ชไปทอยขอ 4 ง King Mongkut's Institute of Technology

การประกาศตวช type 01001012 Principle of Computer Programming *pointer_name type (pointer) คอ ชนดของตวแปรประเภทตวช คอ เครองหมายแสดงวาเปนตวแปรประเภทตวช pointer_name คอ ชอของตวแปรประเภทตวช int *ptr_int; /* pointer to integer */ float *ptr_float; /* pointer to float */ ตวอยางการประกาศตวช char *ptr_char; /* pointer to char */ * Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ 5 King Mongkut's Institute of Technology

ตวดำเนนการ & (สงคาทอย ) 01001012 Principle of Computer Programming &variable • ตวดำเนนการ & ใชสำหรบสงคาทอย (Address) ของตวแปร หรอ วตถ ตวอยางการใชงานตวดำเนนการ 21 EC 21 ED 15 & int count int *ptr int count, *ptr; ptr = &count; /* ptr 21 EC */ Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ เกบตำแหนงของ count มคาเปน 6 King Mongkut's Institute of Technology

ตวอยางการใชตวชเกบตำแหนงตวแปร 01001012 Principle of Computer Programming ทอยของขอ มล )Address) ขอมล ประเภท int ชอตว แปร count ขนาด 2 bytes 0000 15 0002 3. 1415 float pi 4 bytes 0006 'A' char ch 1 bytes 0006 char *ptr_char = &ch; 0002 float *ptr_float = π 0000 int *ptr_int = &count; Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ 7 King Mongkut's Institute of Technology

ตวดำเนนการ * (อางอง ) 01001012 Principle of Computer Programming *pointer_name • ตวดำเนนการ * เปน ตวดำเนนการเชงออม 21 CE (Indirection) หรอ กลบการอางอง (Dereferencing) 21 CF ตวอยางการใชงานตวดำเนนการ * 21 D 0 21 D 1 21 D 2 21 D 3 21 D 4 21 D 5 z[0] z[1] z[2] int count = 15, y, z[10]; int *ptr; */ ptr เปนตวช ��int */ ptr 21 E 2 ptr = &count; */ptr ชไปท ��count 21 E 6 */ y 21 E 7 y =* ptr; */y มคาเทากบคาท 21 E 8 15 count 21 E 9 21 E 8/* Jirasak Sittigorn 8 *ptr = 0; */ คาท 21 E 8 เปน 0 King Mongkut's Institute of Technology http: //www. kmitl. ac. th/~ksjirasa/

ตวอยางโปรแกรมการใช #include<stdio. h> int main() { printf กบตวช (1) 01001012 Principle of Computer Programming letter num point char letter = 'D'; D 19 26. 09 int num = 19; float point = 26. 09; 243 F 243 C 2438 char * pt_letter; int * pt_num; pt_letter pt_num pt_point float * pt_point; pt_letter = & letter; 243 F 243 C 2438 pt_num = & num; pt_point = & point; ? ? ? printf("Address of letter = %p n", pt_letter); printf("Address of num = %p n", pt_num); printf("Address of point = %p n", pt_point); return 0; } Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ 10 King Mongkut's Institute of Technology

ตวอยางโปรแกรมการใช printf กบตวช • ผลลพธการรนโปรแกรม Address of letter = 2523: 243 F Address of num = 2523: 243 C Address of point = 2523: 2438 (2) 01001012 Principle of Computer Programming letter num D 19 point 26. 09 243 F 243 C 2438 pt_letter pt_num pt_point Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ 243 F 243 C 2438 ? ? ? ? 11 King Mongkut's Institute of Technology

ตวอยางโปรแกรมการใช - A (1) referencing และ dereferencing 01001012 Principle of Computer Programming int main() num 1 price 1 hint 1 { 113 4. 85 J int num 1 = 113, num 2; float price 1 = 4. 85; --x-- --y-- --z-char hint 1 = 'J', hint 2; int * pt_num; pt_num pt_price pt_hint float * pt_price; --x---y---z-char * pt_hint; pt_num = &num 1; pt_price = &price 1; num 2 hint 2 pt_hint = &hint 1; num 2 = *pt_num; 113 J hint 2 = *pt_hint; printf ("Variable num 1 = %d n", num 2); printf ("Variable price 1 = %f n", *pt_price); printf ("Variable hint 2 = %c n", hint 2); return 0; Jirasak } Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ 12 King Mongkut's Institute of Technology

ตวอยางโปรแกรมการใช - A (2) • ผลลพธการรนโปรแกรม Variable num 1 = 113 Variable price 1 = 4. 850000 Variable hint 2 = J referencing และ dereferencing 01001012 Principle of Computer Programming num 1 price 1 hint 1 113 4. 85 --x-- --y-- --z-pt_num pt_price pt_hint --x-- Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ J --y-- --z-- num 2 hint 2 113 J 13 King Mongkut's Institute of Technology

ตวอยางโปรแกรมการใช - B (1) referencing และ dereferencing 01001012 Principle of Computer Programming #include<stdio. h> int main() { int a; /* a is an integer */ int *a. Ptr; /* a. Ptr is a pointer to an integer */ a = 7; a. Ptr = &a; /* a. Ptr set to address of a */ printf ("The address of a is %pn" "The value of a. Ptr is %pnn", &a, a. Ptr); printf ("The value of a is %dn" "The value of *a. Ptr is %dnn", a, *a. Ptr); printf ("Proving that * and & are complements of " "each other. n&*a. Ptr = %pn*&a. Ptr = %pn", &*a. Ptr, *&a. Ptr); return 0; } Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ 14 King Mongkut's Institute of Technology

ตวอยางโปรแกรมการใช - B (2) • ผลลพธการรนโปรแกรม FFF 4 7 a referencing และ dereferencing 01001012 Principle of Computer Programming ? ? FFF 4 a. Ptr printf ("The value a is %dn" address of a is ("Proving *an and &%pn" are complements of " int a; /*that aof is integer */ The address of a is FFF 4 "The of *a. Ptr is %dnn", a, = *a. Ptr); "eachvalue other. n&*a. Ptr =%pnn", %pn*&a. Ptr %pn", */ int *a. Ptr; /* a. Ptr is ais pointer to &a, an integer The value of a. Ptr is FFF 4 a = 7; &*a. Ptr, *&a. Ptr); The value ofof a is 7 a. Ptr address a/*is FFF 4 set to address of a */ a. Ptr = &a; The value of *a. Ptr a and is is 7 is Proving that * & FFF 4 are The of 7 complements of each other. a. Ptr The value of *a. Ptr is 7 &*a. Ptr = FFF 4 *&a. Ptr = FFF 4 Proving that * and & are complements of each other. &*a. Ptr = FFF 4 *&a. Ptr = FFF 4 Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ 15 King Mongkut's Institute of Technology

สรปการดำเนนการของตวแปรประเภทตวช 01001012 Principle of Computer Programming การประกาศตวแปรพอยนเต type *อรpt_name; variable 1 แสดงตำแหนงขอมลด pt_name =วย&variable 1; & pt_name แสดงขอมลดวย * variable 2 = *pt_name; Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ d 1906 ---variable 2 d ---16 King Mongkut's Institute of Technology

พอยนเตอรซอนพอยนเตอร (Nested Pointer) (2) 01001012 Principle of Computer Programming ตวอยางการใชงานพอยนเตอรซอนพอยนเตอร float time = 9. 28; float *pt_time; float **ptt_time; time pt_time ptt_time 9. 28 0100 0250 03 AA pt_time = &time; ptt_time = &pt_time; float temp 1; temp 1 = *pt_time; 9. 28 0510 float temp 2; temp 2 = **ptt_time; Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ temp 2 9. 28 05 C 0 18 King Mongkut's Institute of Technology

เลขคณตของตวช (3) 01001012 Principle of Computer Programming v[0] v[1] v[2] v[3] v[4] 2 3 5 7 11 3000 3004 3008 300 C 3010 Object Address v. Ptr float v[5]={2, 3, 5, 7, 11}; ; float* v. Ptr; v. Ptr = &v[0]; v. Ptr += 2; /* v. Ptr = v. Ptr+2 */ v. Ptr += 1; /* v. Ptr = v. Ptr+1 */ v. Ptr -= 3; /* v. Ptr = v. Ptr+3 */ Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ 24 King Mongkut's Institute of Technology

เลขคณตของตวช v[0] 3000 (4) v[1] 3004 v. Ptr v[2] 3008 01001012 Principle of Computer Programming v[3] 300 C v. Ptr+2 Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ v[4] 3010 Object Address v. Ptr+4 25 King Mongkut's Institute of Technology

เลขคณตของตวช • เมอทำการบวก (5) หรอลบ ระหวางตวช คาทไดรบคอจำนวนหนวย v[0] v[1] ของตวแปรแถวลำดบ ตวอยาง 01001012 Principle of Computer Programming 2 3000 3 3004 v[2] v[3] v[4] 5 7 11 3008 float v[5]={2, 3, 5, 7, 11}; float* v 1 Ptr, *v 2 Ptr; int x; v 1 Ptr = &v[0]; // 3000 v 2 Ptr = &v[2]; // 3008 x = v 2 Ptr – v 1 Ptr; printf ("v 2 Ptr – v 1 Ptr = %d", x); Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ (element) 300 C 3010 v 1 Ptr Object Address v 2 Ptr 26 King Mongkut's Institute of Technology

ตวอยางการใชงานตวแปรพอยนเตอร กบอารเรย (1) 01001012 Principle of Computer Programming int num[5] = {12, 34, 112, 45, 907}; *pt_num; num[0] num[1] num[2] num[3] num[4] 12 34 112 45 907 0410 0412 0414 0416 0418 pt_num = &num[1]; pt_num = &num[4]; int temp; temp = *pt_num; pt_num 0412 0418 0350 temp 907 050 A Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ 28 King Mongkut's Institute of Technology

ตวอยางการใชงานตวแปรพอยนเตอร กบอารเรย (2) 01001012 Principle of Computer Programming type name[10]; type *pt_name; pt_name = name; //pt_name = &name[0] float num[] = {19. 01, 26. 09, -4. 23, -4. 24, -13. 12} num[0] num[1] num[2] num[3] num[4] 19. 01 26. 09 -4. 23 -4. 24 -13. 12 0300 0304 0308 030 C 0310 Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ 29 King Mongkut's Institute of Technology

ตวอยางการใชงานตวแปรพอยนเตอร กบอารเรย (3) 01001012 Principle of Computer Programming float *pt_num; num[0] num[1] num[2] num[3] num[4] 19. 01 26. 09 -4. 23 -4. 24 -13. 12 0300 0304 0308 030 C 0310 pt_num = num; float test 1, test 2; test 1 = *(pt_num+3); test 2 = *(pt_num+1); Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ 0300 +3 090 D test 1 test 2 -4. 24 26. 09 032 A 322 E +1 30 King Mongkut's Institute of Technology

ตวอยางโปรแกรมการใช Pointers กบ Arrays (1) 01001012 Principle of Computer Programming int main() { int i, offset, b[] = {10, 20, 30, 40}; int *b. Ptr = b; /* set b. Ptr to point to array b */ printf("Array b printed with: n" "Array subscript notationn"); for (i=0; i<=3; i++) printf("b[%d] = %dn", i, b[i]); return 0; } Array b printed with: Array subscript notation b[0] = 10 b[1] = 20 b[2] = 30 b[3] = 40 Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ 31 King Mongkut's Institute of Technology

ตวอยางโปรแกรมการใช Pointers กบ Arrays (2) 01001012 Principle of Computer Programming int main() { int i, offset, b[] = {10, 20, 30, 40}; int *b. Ptr = b; /* set b. Ptr to point to array b */ printf("Pointer/offset notation wheren" "the pointer is the array namen"); for (offset = 0; offset<=3 ; offset++) printf("*(b + %d) = %dn", offset, *(b + offset)); return 0; } Pointer/offset notation where The pointer is the array name *(b + 0) = 10 *(b + 1) = 20 *(b + 2) = 30 *(b + 3) = 40 Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ 32 King Mongkut's Institute of Technology

ตวอยางโปรแกรมการใช Pointers กบ Arrays (3) 01001012 Principle of Computer Programming int main() { int i, offset, b[] = {10, 20, 30, 40}; int *b. Ptr = b; /* set b. Ptr to point to array b */ printf("Pointer subscript notationn"); for (i=0 ; i<=3 ; i++) printf("b. Ptr[%d] = %dn", i, b. Ptr[i]); return 0; } Pointer b. Ptr[0] b. Ptr[1] b. Ptr[2] b. Ptr[3] subscript notation = 10 = 20 = 30 = 40 Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ 33 King Mongkut's Institute of Technology

ตวอยางโปรแกรมการใช Pointers กบ Arrays (4) 01001012 Principle of Computer Programming int main() { int i, offset, b[] = {10, 20, 30, 40}; int *b. Ptr = b; /* set b. Ptr to point to array b */ printf("Pointer/offset notationn"); for (offset=0; offset<=3; offset++) printf("*(b. Ptr + %d) = %dn", offset, *(b. Ptr + offset)); return 0; } Pointer/offset notation *(b. Ptr + 0) = 10 *(b. Ptr + 1) = 20 *(b. Ptr + 2) = 30 *(b. Ptr + 3) = 40 Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ 34 King Mongkut's Institute of Technology

ตวอยางโปรแกรมการใช Pointers กบ Arrays (5) 01001012 Principle of Computer Programming int main() { int b[10]={0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; int a[10], i, *pt. A, *pt. B; for (i=0; i<10; i++) printf ("%d ", b[i]); a[15] = 100; printf ("nn. Define a[15] = 100"); printf ("na[15] = %dnn", a[15]); for (i=0; i<10; i++) printf ("%d ", b[i]); pt. A = a; pt. B = b; printf ("nn. Address a[0] : %pn", pt. A); printf ("Address b[0] : %pn", pt. B); printf ("Address a[15] : %pn", pt. A+15); printf ("Address b[5] : %pn", pt. B+5); } a[0] 0 2240 b[5] b[0] 2242 2244 2246 2248 224 A Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ 224 C 1 2 3 4 5 6 7 8 9 2250 2254 2258 225 C 2260 2264 224 E 2252 2256 225 A 225 E 2262 2266 35 King Mongkut's Institute of Technology

a. Ptr struct card { char face[6]; // 2, 3, . . , 9, Jack, Queen, King, Ace char suit[8]; // space, heart, diamond, club }; struct card a; struct card *a. Ptr; strcpy(a. face, "Ace"); strcpy(a. suit, "heart"); a. Ptr = &a; printf("face : %sn", a. face); printf("face : %sn", a. Ptr->face); printf("suit : %sn", a. suit); printf("suit : %sn", a. Ptr->suit); printf ("Address of a. face : %pn", &a. face); printf ("Address of a. suit : %pn", &a. suit); Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ a A c e h e a r t a. face • เมอสมาชกในโครงสรางไมใชตวช (2) 01001012 Principle of Computer Programming a. suit ตวชกบตวแปรแบบโครงสราง 37 King Mongkut's Institute of Technology

• เมอสมาชกในโครงสรางเปนตวช (3) 01001012 Principle of Computer Programming a. Ptr struct card { char * face; // 2, 3, . . , 9, Jack, Queen, King, Ace char * suit; // space, heart, diamond, club }; A h struct card a; c e struct card *a. Ptr; e a a. face = "Ace"; r a. suit = "heart"; t a. Ptr = &a; printf("face : %sn", a. face); printf("face : %sn", a. Ptr->face); printf("suit : %sn", a. suit); printf("suit : %sn", a. Ptr->suit); printf ("Address of a. face : %pn", &a. face); printf ("Address of a. suit : %pn", &a. suit); printf ("Value of a. face : %pn", a. face); printf ("Value of a. suit : %pn", a. suit); Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ a 0 0 7 6 0 0 7 A a. suit a. face ตวชกบตวแปรแบบโครงสราง 38 King Mongkut's Institute of Technology

• เมอสมาชกในโครงสรางเปนตวช (4) 01001012 Principle of Computer Programming a. Ptr struct card { char * face; // 2, 3, . . , 9, Jack, Queen, King, Ace char * suit; // space, heart, diamond, club }; Q h struct card a; u e struct card *a. Ptr; e a a. face = "Queen"; e r a. suit = "heart"; t n a. Ptr = &a; printf("face : %sn", a. face); printf("face : %sn", a. Ptr->face); printf("suit : %sn", a. suit); printf("suit : %sn", a. Ptr->suit); printf ("Address of a. face : %pn", &a. face); printf ("Address of a. suit : %pn", &a. suit); printf ("Value of a. face : %pn", a. face); printf ("Value of a. suit : %pn", a. suit); Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ a 0 0 7 6 0 0 7 C a. suit a. face ตวชกบตวแปรแบบโครงสราง 39 King Mongkut's Institute of Technology

ตวอยางการใชตวชกบตวแปรแบบโครงสราง (1) 01001012 Principle of Computer Programming int main(){ struct card { char * face; char * suit; }; // 2, 3, . . , 9, Jack, Queen, King, Ace // space, heart, diamond, club struct card a; struct card *a. Ptr; a. face = "Ace"; a. suit = "spade"; a. Ptr = &a; printf( "%s %s %sn%s %s %sn", a. face , "of" , a. suit, a. Ptr->face , "of" , a. Ptr->suit, (*a. Ptr). face , "of" , (*a. Ptr). suit ); return 0; a. Ptr } Ace of spade Ace Spade pppp+4 Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ a xxxx a. face a. suit pppp+4 xxxx yyyy 40 King Mongkut's Institute of Technology

ตวอยางการใชตวชกบตวแปรแบบโครงสราง (2) 01001012 Principle of Computer Programming int main(){ struct card { char * face; char * suit; }; // 2, 3, . . , 9, Jack, Queen, King, Ace // space, heart, diamond, club struct card a; struct card *a. Ptr; a. face = "A"; a. suit = "spade"; a. Ptr = &a; printf( "%s %s %sn%s %s %sn", a. face , "of" , a. suit, a. Ptr->face , "of" , a. Ptr->suit, (*a. Ptr). face , "of" , (*a. Ptr). suit ); return 0; } a. Ptr xxxx pppp Ace of spade Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ A Spade pppp+2 a a. face a. suit pppp+2 xxxx yyyy 41 King Mongkut's Institute of Technology

โปรแกรมเกบขอมลตวละครจำนวน – ตวอยางการรนโปรแกรม Character 1 name age Character 2 name age Character 3 name age Character 4 name age Character 5 name age Character 6 name age Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ : Gon : 12 : Kuroro : 26 : Hisoka : 27 : Killua : 12 : Machi : 24 : Nobunaga : 30 10 คน (2) 01001012 Principle of Computer Programming Character 7 name : age : Character 8 name : age : Character 9 name : age : Character 10 name : age : Kurapica 17 Ubogin 29 Pakunoda 28 Leorio 19 Gon, 12 Killua, 12 Kurapica, 17 Leorio, 19 43 King Mongkut's Institute of Technology

โปรแกรมเกบขอมลตวละครจำนวน 10 คน | Pointer (3) 01001012 Principle of Computer Programming #include<stdio. h> #define N 10 int main() { int i; struct profile{ char name[30]; int age; }p[N]; struct profile *p. Ptr; p. Ptr = p; //continue Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ 44 King Mongkut's Institute of Technology

โปรแกรมเกบขอมลตวละครจำนวน 10 คน | Pointer (4) 01001012 Principle of Computer Programming for(i=0; i<N; i++, p. Ptr++) { printf("Character %dn", i+1); printf("tname : "); scanf("%s", p. Ptr->name); printf("tage : "); scanf("%d", &(p. Ptr->age)); } p. Ptr-=N; for(i=0; i<N; i++, p. Ptr++) if(p. Ptr->age < 20) printf("n %s, %d", p. Ptr->name, p. Ptr->age); return 0; } Jirasak Sittigorn http: //www. kmitl. ac. th/~ksjirasa/ 45 King Mongkut's Institute of Technology