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

void die(const char *message)
{
  if(errno) {
    perror(message);
  } else {
    printf("ERROR: %s\n", message);
  }

  exit(1);
}

int main(int argc, char *argv[]) {
  const double yins = 0.067;
  const double siny = 14.91;
  if(argc < 2) die("USAGE: <currency option> <value to convert>");
  char curr = argv[1][0];
  char *ammount_str = argv[2];
  double ammount;
  sscanf(ammount_str, "%lf", &ammount);
  double converted;

  if(curr == 'y') {
    converted = ammount * siny;
    printf("%f SEK is equal to %f yen.\n", ammount, converted);
  } else if(curr == 's') {
    converted = ammount * yins;
    printf("%f yen is equal to %f SEK.\n", ammount, converted);
  } else die("Invalid currency option.");

  return 0;
}