#include "library.h"

const string alpha = "abcdefghijklmnopqrstuvwxyz ";
const string randa = "hurdmyboxkgavsejcpzwinltqf ";

int find_pos(const string S, const char C, const int start)
            // S = string to search through
            // C = character to search for
            // start = where to start the search
{ if (start >= S.length())
    return -1;
  if (S[start] == C)
    return start;
  return find_pos(S, C, start + 1); }

char translate(const char C, const string al, const string ra)
       // find pos of C in al, return char at that position in ra
{ const int pos = find_pos(al, C, 0);
  if (pos == -1)
    return '?';
  return ra[pos]; }

string translate(const string S, const string al, const string ra)
{ if (S == "")
    return "";
  const char c1 = translate(S[0], al, ra);
  const string s2 = translate(S.substr(1), al, ra);
  const string empty = "";
  return empty + c1 + s2; }

void main()
{ cout << "Encrypt = E or Decrypt = D? ";
  const string choice = read_line();
  cout << "Enter a string: ";
  const string x = read_line();
  if (choice == "E")
    cout << translate(x, alpha, randa) << "\n";
  else if (choice == "D")
    cout << translate(x, randa, alpha) << "\n";
  main(); }