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Con tr

Bi 8

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Elementary Programming with C/Session 8/ Slide 2 of 30

Mc tiu bi hc

Tm hiu v con tr v khi no th s dngcon tr

Cch s dng bin con tr v cc ton t con

trGn gi tr cho con trPhp ton trn con tr

So snh con trCon tr v mng mt chiuCon tr v mng nhiu chiu

Tm hiu cch cp pht b nh

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Con tr l g?

Con tr l mt bin, n cha a ch nh camt bin khc

Nu mt bin cha a ch ca mt bin khc,

th bin ny c gi l con tr tr nbin thhai

Con tr cung cp phng thc truy xut gin

tip n gi tr ca mt phn t d liuCc con tr c th tr n cc bin c kiu d

liu c bn nh int, char,double, hay d liu tphp nh mnghoc cu trc.

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Con tr c s dng lm g?

Cc tnh hung con tr c th c s dng: tr v nhiu hn mt gi tr t mt hm

truyn mng v chui t mt hm nmt hm khc thun tin hn lm vic vi cc phn t ca mng thay

v truy xut trc tip vo cc phn t ny cp pht b nh v truy xut b nh

(Cp pht b nh trc tip)

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Bin con tr

Khai bo con tr: ch ra mt kiu c s vmt tn bin c t trc bi du *

C php khai bo tng qut:

V d:

type *name;

int *var2;

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Cc ton t con tr

Hai ton t c bit c s dng vi con tr:

& l ton t mt ngi v n tr v a ch nhca ton hng

Ton t *l phn b xung ca ton t &. y l

ton t mt ngi v n tr v gi tr cha trongvng nh c tr n bi bin con tr

v& *

var2 = &var1;

temp = *var2;

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7/30Elementary Programming with C/Session 8/ Slide 7 of 30

Gn tr i vi con tr

Cc gi tr c th c gn cho con trthng qua ton t &.

ptr_var = &var;

y a ch ca var c lu vo binptr_var.

Cng c th gn gi tr cho con tr thngqua mt bin con tr khc tr c cngkiu. ptr_var = &var;

ptr_var2 = ptr_var;

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C th gn gi tr cho cc bin thngqua con tr

*ptr_var = 10;

Cu lnh trn gn gi tr 10 cho binvar nu ptr_var ang tr n var

Gntr i vi con tr (tt)

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Php ton con tr Ch c th thc hin php ton cng v tr trn

con trint var, * ptr_var;

ptr_var = & var;var = 500;

ptr_var ++;

Gi s bin varc lu tr ti a ch 1000 ptr_var lu gi tr 1000. V s nguyn c kch

thc l 2 bytes, nn sau biu thcptr_var++; ptr_var s c gi tr l 1002 m

khng l 1001

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Php ton con tr (tt)

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Mi ln con tr c tng tr, n tr n nh caphn t k tip

Mi ln con tr c gim tr, n tr n nhca phn t ng trc n

Tt c con tr s tng hoc gim tr theo kchthc ca kiu d liu m chng ang tr n

Php ton con tr (tt)

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So snh con tr

Hai con tr c th c so snh trong mt biuthc quan h nu chng tr n cc bin c cngkiu d liu

Gi s ptr_a v ptr_b l hai bin con tr tr n ccphn t d liu a v b. Trong trng hp ny, ccphp so snh sau l c th:

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So snh con tr (tt)

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Con tr v mng mt chiu

a ch ca mt phn t mng c th cbiu din theo hai cch:

S dng k hiu & trc mt phn tmng. S dng mt biu thc trong ch s

ca phn t c cng vo tn ca

mng.

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#include

void main(){

static int ary[10]

={1,2,3,4,5,6,7,8,9,10};

int i;for (i= 0;i

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Con tr v mng mt chiu-v d tt

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Mng hai chiu c th c nh ngha nh lmt con tr tr ti mt nhm cc mng mtchiu lin tip nhau

Khai bo mt mng hai chiu c th nh sau:

thay v

data_type (*ptr_var) [expr 2];

data_type (*ptr_var) [expr1] [expr 2];

Con tr v mng a chiu

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Con tr v chui#include #include

void main (){

char a, str[81], *ptr;

printf(\nEnter a sentence:);

gets(str);printf(\nEnter character to search for:);

a = getche();

ptr = strchr(str,a);

/* return pointer to char*/

printf( \nString starts at address: %u,str);printf(\nFirst occurrence of the character is

at address: %u ,ptr);

printf(\n Position of first occurrence(starting

from 0)is: % d, ptr_str);

}

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Con tr v chui (tt)

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Cp pht b nh

Hm malloc() l mt trong cc hm c s

dng thng xuyn nht thc hin vic cp

phtbnht vng nhcn t do.

Tham sca hm malloc() l mts nguyn xc

nhs bytes cncp pht.

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Cp pht b nh (tt)

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Hm free()

Hm free() c s dng gii phng bnh khi n khng cn dng na.C php:

void free(void*ptr);Hm ny gii phng khng gian c tr biptr, dng cho tng lai.

ptrphi c dng trc vi li gi hmmalloc(), calloc(), hoc realloc().

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#include #include /*required for the malloc and free functions*/

int main(){

int number;

int *ptr;int i;

printf("How many ints would you like store? ");

scanf("%d", &number);

ptr = (int *) malloc (number*sizeof(int));

/*allocate memory */

if(ptr!=NULL) {

for(i=0 ; i

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for(i=number ; i>0 ; i--) {

printf("%d\n",*(ptr+(i-1)));

/* print out in reverse order */

}

free(ptr); /* free allocated memory */return 0;

}

else {

printf("\nMemory allocation failed -

not enough memory.\n");

return 1;

}

}

Hm free() - tt

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Hm calloc()

calloctng t nh malloc, nhng im khc bitchnh l mc nhin gi tr 0 c lu vo khng gian

b nh va cp pht

callocyu cu hai tham s Tham s th nht l s lng cc bin cn cp pht

b nh Tham s th hai l kch thc ca mi binC php:

void *calloc( size_t num, size_t size );

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#include #include

int main() {

float *calloc1, *calloc2;

int i;

calloc1 = (float *) calloc(3,

sizeof(float));

calloc2 = (float *)calloc(3, sizeof(float));

if(calloc1!=NULL && calloc2!=NULL){

for(i=0 ; i

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free(calloc1);

free(calloc2);

return 0;

}else{

printf("Not enough memory\n");

return 1;

}}

Hm calloc() - tt

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Hm realloc()

C th cp pht li cho mt vng c cp (thm/bts bytes) bng cch s dng hm realloc, m khng lmmt d liu.

reallocnhn hai tham s Tham s th nht l con tr tham chiu n b nh

Tham s th hai l tng s byte mun cp pht C php:void *realloc( void *ptr, size_t size );

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#include

#include

int main(){

int *ptr;

int i;ptr = (int *)calloc(5, sizeof(int *));

if(ptr!=NULL) {

*ptr = 1; *(ptr+1) = 2;

ptr[2] = 4; ptr[3] = 8; ptr[4] = 16;

ptr = (int *)realloc(ptr, 7*sizeof(int));if(ptr!=NULL){

printf("Now allocating more memory...\n");

ptr[5] = 32; /* now it's legal! */

ptr[6] = 64;

Hm realloc() - tt

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for(i=0;i

session 08

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