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

struct element
{   string name, symbol;
    double weight; };

const int max_table_size = 110;

struct periodic_table
{ element table[max_table_size];
  int num_elements; };

void make(periodic_table & t)
{ t.num_elements=0; }

element make(string s, string n, double w)
{   element r;
    r.symbol=s;
    r.name=n;
    r.weight=w;
    return r; }

element find_symbol(periodic_table t, string s)
{ for (int i=0; i<t.num_elements; i+=1)
  { if (t.table[i].symbol == s)
    { return t.table[i]; } }
  return make("?", "!!!error!!!", -999999); }

void print(element e)
{ cout << e.name
       << " (" << e.symbol 
       << ") w=" << e.weight << "\n"; }

void read(periodic_table & t)
{  ifstream efile("elements.txt");
   if (efile.fail())
   {  cerr << "Can't open 'elements.txt'\n";
      exit(1); }
   for (int i=0; i<max_table_size; i+=1)
   { string sy, nm;
     double wt;
     efile >> sy >> nm >> wt;
     if (efile.fail())
        break;
     t.table[i]=make(sy, nm, wt);
     t.num_elements=i; }
   efile.close(); }

struct inputthing
{ string formula;
  int pos; };

void read(inputthing & x, string prompt="")
{ cout << prompt;
  cin >> x.formula;
  x.pos=0; }

string combine(char a, char b=0)
{ string s="";
  s+=a;
  if (b!=0)
    s+=b;
  return s; }

char nextchar(inputthing & w)
{ if (w.pos>=w.formula.length())
  { w.pos+=1;
    return '*'; }
  char c=w.formula[w.pos];
  w.pos+=1;
  return c; }

void putcharback(inputthing & w)
{ w.pos-=1; }

struct item
{ string str;
  int num;
  char which; /* 'S' means string, 'N' means number */ };

item makeitem(char w)
{ item r;
  r.which=w;
  return r; }

item makeitem(string s)
{ item r;
  r.str=s;
  r.which='S';
  return r; }

item makeitem(int n)
{ item r;
  r.num=n;
  r.which='N';
  return r; }

item nextsymbol(inputthing & x)
{ char c1=nextchar(x);

  if (c1=='*')
    return makeitem('*');

  else if (c1=='(')
    return makeitem('(');

  else if (c1==')')
    return makeitem(')');

  else if (c1>='A' && c1<='Z')
  { char c2=nextchar(x);
    if (c2>='a' && c2<='z')
      return makeitem(combine(c1, c2));
    putcharback(x);
    return makeitem(combine(c1)); }

  else if (c1>='0' && c1<='9')
  { int value = c1 - '0';
    char c2=nextchar(x);
    while (c2>='0' && c2<='9')
    { value = value * 10 + c2 - '0';
      c2=nextchar(x); }
    putcharback(x);
    return makeitem(value); }

  else
    return makeitem('?'); }

double molecular_weight(periodic_table PT, inputthing & reader)
{ double total=0.0, last=0.0, memory=0.0;
  while (true)
  { item it = nextsymbol(reader);

    if (it.which=='*')
      break;

    else if (it.which=='(')
    { memory=total;
      total=0; }

    else if (it.which==')')
    { last=total;
      total+=memory; }

    else if (it.which=='S')
    { element e = find_symbol(PT, it.str);
      last=e.weight;
      total+=last; }

    else if (it.which=='N')
    { total+=last*(it.num-1); }

    else if (it.which=='?')
    { cerr << "It doesn't make sense\n";
      total=-999999;
      break; } }
    
  return total; }
	
void main()
{ periodic_table PT;
  make(PT);
  read(PT);
  inputthing reader;
  read(reader, "formula: ");
  double total=molecular_weight(PT, reader);
  cout << "molecular weight = " << total << "\n"; }