knr/5.6.c

#include <stdio.h>
/*

rewrite reverse from chapter 3 to use pointers.
*/

/* reverse:  reverse string s in place */
char* reverse(char* s);
void testreverse();

int main ()
{
  testreverse();
  return(0);
}

void testreverse()
{
  char p1[] ="123456789";
  printf("%s \n",reverse(p1));
}

char* reverse(char s[])
{
  char* tmpstr=s;
  char* retstr=s;
  for (int i=0;*tmpstr!=0;i++)
    tmpstr++;
  tmpstr--;    //back into the string

  char temp=0; //temp for swapping

  while (retstr!=tmpstr)
  {
    temp=*retstr;
    *retstr=*tmpstr;
    *tmpstr=temp;

    retstr++;
    tmpstr--;
  }
  return s;
}