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

#define ENCODE_STARTCHAR 32
#define ENCODE_ENDCHAR	 126



int encode(const char *key, const char *text, char *out, size_t outbuflen)
{
  int i;
  i = 0;
  
  int key_size = strlen(key);
  
  while(text[i] && i < outbuflen)
    {
      out[i] = ((text[i] - ENCODE_STARTCHAR) + (key[i%key_size] - ENCODE_STARTCHAR)) % (ENCODE_ENDCHAR - ENCODE_STARTCHAR + 1) + ENCODE_STARTCHAR;
      printf("%c + %c -> %c\n", text[i], key[i%key_size], out[i]);
      i++;
    }
  if (i < outbuflen)
    out[i] = '\0';
  return 0;
}

int decode(const char *key, const char *text, char *out, size_t outbuflen)
{
  int i;
  i = 0;
  
  int key_size = strlen(key);
  
  while(text[i] && i < outbuflen)
    {
      out[i] = (((text[i] - ENCODE_STARTCHAR) - (key[i%key_size] - ENCODE_STARTCHAR)) +
		ENCODE_ENDCHAR - ENCODE_STARTCHAR + 1) % (ENCODE_ENDCHAR - ENCODE_STARTCHAR + 1) + ENCODE_STARTCHAR;
      printf("%c + %c -> %c\n", text[i], key[i%key_size], out[i]);
      i++;
    }
  if (i < outbuflen)
    out[i] = '\0';
  return 0;
}


int main()
{
  char merong[100];
  char merong2[100];
  printf("plain text: %s\n", "Meet me in St. Louis");
  encode("Walrus", "Meet me in St. Louis", merong, 100);
  printf("encoded: %s\n", merong);
  decode("Walrus", merong, merong2, 100);
  printf("decoded: %s\n", merong2);
  return 0;
}