Pointer to Strings (Pointers Part 3)

                      Pointer to strings

 Declaration of pointer to strings:

char  str[6]=”HELLO”;

 

 str[0]                     str[1]             str[2]          str[3]     str[4]          str[5]

H

E

L

L

O

\0

Addressà        1000 1001            1002          1003       1004         1005

 

str à name of the string à base address of the string à 1000

( str + 0 ) à ( 1000 + 0*1) à 1000 à&str[0]

( str + 1 ) à ( 1000 + 1*1) à 1001 à&str[1]

( str + 2 ) à ( 1000 + 2*1) à 1002 à&str[2]

( str + 3 ) à ( 1000 + 3*1) à 1003 à&str[3]

 

Here scale factor value is 1, since size of char is only one byte.

 

*( str + 0 ) à *( 1000 + 0*1) à *(1000) à str[0]  à value

*( str + 1 ) à *( 1000 + 1*1) à *(1001) à str[1]à value

*( str + 2 ) à*( 1000 + 2*1) à*(1002)àstr[2]à value

 

 

int a;

float b;

char str[10];

 

scanf(“%d %f  %s”, &a, &b, str);

 

here for str & is not required, as string name itself is an address of string.

Some programs based on this address of the string using the topic called pointer to strings:

 

#include<stdio.h>

int main()

{

 char str[6]="hello";

 int i;

for(i=0;*(str+i)!='\0';i++)

            {

     printf("%c",*(str+i));

 }

 getch();

 }

 

#include<stdio.h>

int main()

{

 char str[6]="hello";

 int i;

  for(i=4;i>=0;i--)

            {

               printf("%c",*(str+i));

            }

 getch();

 }

 

#include<stdio.h>

int main()

{

 char str[6]="hello";

 int i;

            for(i=4;i>=0;i--)

            {

            printf("%c",*(&str[i]-i));

            }

 getch();

 }

 

Declaring pointer to strings:

 

char str[6];

 

char * ptr;

  ptr=str;   -à here ptr contains base address of string.

 

 

 Program to declare a pointer to a String:

#include<stdio.h>

int main()

{

charstr[6]="hello";

char * ptr;

            for(ptr=str;*ptr!='\0';ptr++)

            {

            printf("%c",*ptr);

            }

 getch();

 }

 

 

#include<stdio.h>

int main()

{

 char str[6]="hello";

 int i;

 char * ptr;

 

            for(ptr=(str+4);ptr>=str;ptr--)

            {

               printf("%c",*ptr);

            }

 getch();

 }

 

Finding length of the string using pointer:

 

#include<stdio.h>

#include<conio.h>

int main()

{

  char str[50];

  char *ptr;

  int c;

  printf("\nEnter a string");

  scanf("%s",str);

  for(ptr=str,c=0;*ptr!='\0';ptr++)

  {

     c++;

  }

 

  printf("\nlength = %d",c);

  getch();

}

 

Copying strings using pointers:

 

#include<stdio.h>

int main()

{

 char str1[6]="hello";

 char str2[6];

 char *ptr1;

 char *ptr2;

            for(ptr1=str1,ptr2=str2;*ptr1!='\0' ;ptr1++,ptr2++)

            {

                *ptr2=*ptr1;

            }

 

            *ptr2='\0';

 

            printf("\n after copying str1=%s and str2=%s",str1,str2);

 getch();

 }

 

Finding length of the string using pointer:

 

#include<stdio.h>

int main()

{

 char str[50];

 int count;

 char *ptr;

            printf("\nEnter a string");

            scanf("%s",str);

 

            for(ptr=str,count=0;*ptr!='\0' ;ptr++,count++);

 

            printf("\n lenght of the string = %d ",count);

 getch();

 }

To make the reverse of the string using pointer:

 

#include<stdio.h>

#include<conio.h>

int main()

{

  char str[50];

  char *ptr1,*ptr2;

  char temp;

  printf("\nEnter a string");

  scanf("%s",str);

 

  for(ptr2=str;*ptr2!='\0';ptr2++);

 

  for(ptr1=str,ptr2=ptr2-1;ptr1<ptr2;ptr1++,ptr2--)

  {

      temp=*ptr1;

      *ptr1=*ptr2;

      *ptr2=temp;

 

  }

 

  printf("\n reverse %s ",str);

  getch();

}

 

Note: The Programs given here are pre compiled and pre verified and runned