main.c

#include <stdio.h>
#include <string.h>
#include <ctype.h>

static char buf[] = "the world helorow";

static void revstr(char *start, char *end) {
  register char temp;
  while(start < end) { 
      temp = *start;
      *start++ = *end; 
      *end-- = temp; 
  }
}

int main(int argc, char **argv) {
  register char *end, *x, *y;

  printf("Original string --- %s\n",buf);

  end = &buf[strlen(buf)];

  revstr(buf,end-1);

  printf ("Reversed --- %s\n",buf);

  x = y = buf;

  while(x++ < end) {
    if(/* !isalnum(*x) || */ isspace(*x) || iscntrl(*x)) {
      revstr(y,x-1);
      y = x+1;
    }
  } 

  printf("Processed string --- %s\n",buf);
  
  return(0);
}