Reverse a String without using C functions

char * rev_string (char * str)

{

char temp;

int i , j;

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

for(j = 0 ; j < i ; j++ , i--)

{

      temp = str[j];

      str[j] = str[i];

      str[i] = temp;

}

return str;

}