#include <stdio.h>

 #include <string.h>

 void cvtstring(char * pStr)

 {

     if(NULL == pStr)

     {

         return ;

     }

     int iLen = strlen(pStr);

     int iStart = , iStop = iLen / ;

     int i  = ;

     for(i = iStart; i < iStop;i++)

     {

         char x = pStr[i];

         /*printf("x = %c\n", x);*/

         pStr[i] = pStr[iLen -  - i];

         pStr[iLen -  - i] = x;

     }

 }

 int main()

 {

     char p[] = {"hello world"};

     printf("src : [%s]\n", p);

     cvtstring(p);

     printf("dst : [%s]\n\n", p);

     printf("src : [%s]\n", p);

     cvtstring(p);

     printf("dst : [%s]\n", p);

     return ;

 }

$ g++ -o cvtstring cvtstring.cpp

$ ./cvtstring

src : [hello world]

dst : [dlrow olleh]

src : [dlrow olleh]

dst : [hello world]