#include <iostream>
#include <fstream>
#include <iomanip>
#include <string>

using namespace std;

struct input
{ string line;
  int pos, len;
  char kind;       // '.' for '.', 'N' for number, 'S' for symbol
  int which_number;
  string which_symbol; };

void prepare(input & i, string s)
{ i.line = s + ".";
  i.pos = 0;
  i.len = s.length(); }

char next(input & i)
{ while (i.line[i.pos] <= ' ')
    i.pos += 1;

  if (i.line[i.pos] == '.')
    i.kind = '.';

  else if (i.line[i.pos] >= 'A' && i.line[i.pos] <= 'Z')
  { i.kind = 'S';
    i.which_symbol = i.line[i.pos];
    i.pos += 1;
    if (i.line[i.pos] >= 'a' && i.line[i.pos] <= 'z')
    { i.which_symbol += i.line[i.pos];
      i.pos += 1; } }

  else if (i.line[i.pos] >= '0' && i.line[i.pos] <= '9')
  { i.kind = 'N';
    i.which_number = 0;
    while (i.line[i.pos] >= '0' && i.line[i.pos] <= '9')
    { i.which_number = i.which_number * 10 + i.line[i.pos] - '0';
      i.pos += 1; } }

  else
  { cerr << "Incorrect input item beginning with " << i.line[i.pos] << "\n";
    i.kind = '?'; }
  return i.kind; }

string get_symbol(input i)
{ if (i.kind != 'S')
    cerr << "asking for symbol when not\n";
  return i.which_symbol; }

int get_number(input i)
{ if (i.kind != 'N')
    cerr << "asking for number when not\n";
  return i.which_number; }

struct element
{ string name, sym;
  int atno;
  double atwt; };

int read_data(element table[], int tabsize)
{ ifstream fi("elements.txt");
  if (fi.fail())
  { cerr << "Can not open elements.txt\n";
    return 0; }
  table[0].atno = 0;
  table[0].atwt = 0.0;

  int n = 1;
  while (true)
  { string name, symbol;
    int number;
    double weight;

    fi >> number >> name >> symbol >> weight;
    if (fi.fail())
      break;

    table[n].atno = number;
    table[n].name = name;
    table[n].sym = symbol;
    table[n].atwt = weight;

    n += 1; }

  fi.close();
  return n; }

element find_element(string sym, element table[], int tabsize)
{ for (int i = 1; i < tabsize; i += 1)
    if (table[i].sym == sym)
      return table[i];
  return table[0]; }

bool process_formula(element table[], int tabsize)
{ double molwt = 0.0, prev_atwt = 0.0;
  input in;
  while (true)
  { cout << "> ";
    string s;
    getline(cin, s);
    prepare(in, s);
    while (true)
    { char k = next(in);

      if (k == 'S')
      { cout << "Symbol " << get_symbol(in) << "\n";
        element e = find_element(get_symbol(in), table, tabsize);
        if (e.atwt == 0)
          cout << "not found\n";
        else
          cout << e.sym << ", wt = " << e.atwt << "\n";
        prev_atwt = e.atwt;
        molwt += e.atwt; }

      else if (k == 'N')
      { cout << "Number " << get_number(in) << "\n";
        molwt += (get_number(in) - 1) * prev_atwt; }
        
      else if (k == '.')
      { cout << "dot for end\n";
        break; }
        
      else if (k == '?')
        break;
        
      else
        cout << "error return " << k << "\n"; }
    cout << "molecular weight now " << molwt << "\n"; }

  cout << "Total molecular weight is " << molwt << "\n";
  return true; }

int test()
{ input in;
  while (true)
  { cout << "> ";
    string s;
    getline(cin, s);
    prepare(in, s);
    while (true)
    { char k = next(in);
      if (k == 'S')
        cout << "Symbol " << get_symbol(in) << "\n";
      else if (k == 'N')
        cout << "Number " << get_number(in) << "\n";
      else if (k == '.')
      { cout << "dot for end\n";
        break; }
      else if (k == '?')
        break;
      else
        cout << "error return " << k << "\n"; } } }

int main()
{ const int tabsize = 120;
  element table[tabsize];
  int num = read_data(table, tabsize);
  cout << num << " elements read\n";
  if (num == 0)
  { cerr << "No elements have been discovered yet\n";
    exit(1); }

  while (true)
  { bool ok = process_formula(table, tabsize);
    if (! ok)
      break; }
  return 0; }