_jawahir_

 Profile Answers by _jawahir_ 

• Jun 17th, 2011

 

#include<stdio.h>

#include<conio.h>

main()

{

char *str;

int i;

clrscr();

printf("Enter a string");

gets(str);

for(i=0;str[i]!='';i++);

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

putchar(str[i]);

getch();

}

shiva

• Sep 27th, 2011

 

We can use directly strrev ()

Code
 


#include <string.h>


#include <stdio.h>


 


int main(void)


{


   char *forward = "string";


 


   printf("Before strrev(): %s


", forward);


   strrev(forward);


   printf("After strrev():  %s


", forward);


   return 0;


}


 

jbode

 Profile Answers by jbode Questions by jbode

• Dec 14th, 2011

 

Below is a simple, straightforward, maybe not the fastest method for reversing a string in place.

Why not start j at strlen(str) - 1? If the string is empty, strlen will return 0, and since size_t is an unsigned type, 0 - 1 will result in some huge value, inevitably leading to a segmentation fault when we try to write to that location.

Code
#include <stdio.h>


#include <string.h>


#include <assert.h>


 


/**


 * Reverse a string in place.  str must point to 


 * a writable buffer (i.e., not a string constant)


 */


void reverse(char *str)


{


  size_t i,j;


 


  assert(str != NULL);


 


  for(i = 0, j = strlen(str); i < j; i++)


  {


    char tmp = str[--j];


    str[j] = str[i];


    str[i] = tmp;


  }


}