#include "library.h"

const string digs = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";

string convert_to(int Base, int N)
{ if (N >= Base)
    return convert_to(Base, N / Base) + digs[N % Base];
  return string("") + digs[N % Base]; }

int find_pos(char c, string s, int curr_pos)
{ if (curr_pos >= s.length())
  { print("Bad digit '"); print(c); print("'\n");
    return -1; }
  if (s[curr_pos] == c)
    return curr_pos;
  return find_pos(c, s, curr_pos + 1); }

int find_pos(char c, string s)
{ return find_pos(c, s, 0); }

int convert_from(int Base, string Num, int curr_pos, int curr_power)
{ const int this_digit = find_pos(Num[curr_pos], digs);
  const int addition = this_digit * curr_power;
  if (curr_pos == 0)
    return addition;
  return convert_from(Base, Num, curr_pos - 1, curr_power * Base) + addition; }

int convert_from(int Base, string Num)
{ return convert_from(Base, Num, Num.length() - 1, 1); }

void test()
{ print("N from_base to_base? ");
  const string num = read_string();
  const int from = read_int();
  const int to = read_int();
  const int value = convert_from(from, num);
  const string result = convert_to(to, value);
  print(num);
  print(" base ");
  print(from);
  print(" is ");
  print(result);
  print(" base ");
  print(to);
  new_line();
  test(); }

void main()
{ test(); }