/* The plan:

A. Read the entire file into an array of structs

B. Given a symbol, be able to search the array to find
   the corresponding element's data

C. Split a chemical formula such as Na2SO4 into its 
   component parts: symbol Na, multiplier 2, symbol S,
   symbol O, multiplier 4

D. Combine B and C to calculate molecular weights

E. Print results nicely in a text file.
                                         */

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

using namespace std;

struct element
{ int atno;
  string symbol;
  string name;
  double atwt; };

// The next function implements part A

int read_file(element A[], int arr_size)  // returns actual number read.
{ ifstream f("/home/www/class/een118/atwt.txt");
  if (f.fail())
  { cout << "Failed to open atwt.txt file\n";
    exit(1); }
  int i = 1;
  while (i<arr_size)
  { string sym, name;
    double wt;
    f >> sym >> name >> wt;
    if (f.fail())
      break;
    A[i].atno = i;
    A[i].symbol = sym;
    A[i].name = name;
    A[i].atwt = wt;
    i += 1; }
  if (! f.fail())
    cout << "Warning!!!! too many elements\n";
  f.close();
  return i - 1; }

// The next function implements part B

int lookup(string sym, element T[], int num)  // returns position in array
                                              // or -1 for "not found"
{ for (int i=1; i<=num; i+=1)
  { if (T[i].symbol == sym)
      return i; }
  cout << sym << " not found\n";
  return -1; }

int main()
{ element table[110];
  int num_els = read_file(table, 110);

  while (true)   // this loop tests parts A and B.
  { string s;
    cin >> s;
    int pos = lookup(s, table, num_els);
    if (pos>0)
    { element e = table[pos];
      cout << "name = " << e.name << ", number = " << e.atno << "\n"; } } }