#include <stdio.h>


char * reverse(char * str){
  char c;
  int length = 0;

  while (str[length] != '\0'){
    length++;
  }

  for (int i = 0; i < length; i++){

    c = str[0];
    int n;
    for (n = 0; n < (length - i - 1); n++) {
      str[n] = str[n+1];
    }
    str[n] = c;
  }
  return str;
}


int main(int argc, char ** argv){

  char * s = argv[1];

  printf("s = %s  rev(s) = %s\n", s, reverse(s));

}