Thread: scanning the string

Hello, I have a little question, I need to write a function which receives a string as a parameter (like molecular formula "H2O, C6H12O6, ..." ) and has to do 2 things:
1: has to check that an element always starts with a capital letter and may be followed by a single lower case character like Fe2O3
2:the abscence of a number indicates a single atom of that element. for example CO2

I was thinking of using string length method but don't seem to have any luck, any ideas?

thanks for replaying, the thing is that the string can be like H2O, Fe2O3, CO2, not specifically letters followed by numbers

Originally Posted by Nino Meh

thanks for replaying, the thing is that the string can be like H2O, Fe2O3, CO2, not specifically letters followed by numbers

So? Just think about it, you wont get anywhere unless you adapt and combine existing methods to solve your problems.
You have to run a loop.
Check for a string.
If the stream fails, clear the error and get a number.
Decide what to do, depending on whether it is a string or a number.

You may need a state machine like structure for complex formulae.

this is what i have so far

Code:

#include <iostream>
#include <cstdlib>
#include <fstream>
#include <string>
#include <cmath>
#include <cctype>
using namespace std;
const int SIZE = 25;
class CElement
{
public:
    string atomicSymbol;
    int atomicNumber;
    float atomicMass;
};
void readPeriodicTable(CElement [], int &);
void bubbleSort(CElement [], int );
void printTable(CElement [], int &);
void promptUser();
float numberOfGramrsPerMole(CElement [], string);
int findMassNumber(string);
double calculateNumberOfParticles(float, float);

int main()
{
    int num;
    float weight;
    string molecularFormula;
    CElement chemicalelement[SIZE];
    readPeriodicTable(chemicalelement, num);
    bubbleSort(chemicalelement, num);
    printTable(chemicalelement, num);
    promptUser();
    cin >> molecularFormula >> weight;
    return 0;
}// end main

/* Function readPeriodicTable: reads in the data from a file and puts it into an
 * array chemicalelement[]
 * Called by: main
 * Calls: none
 */
void readPeriodicTable(CElement chemicalelement[], int &num)
{
    int count;
    ifstream infile;
    infile.open("periodicTable.txt");
    if ( !infile.is_open() )
    {
        cout << endl << "ERROR: Unable to open file!" << endl;
        system("PAUSE");
        exit(1);
    }
    count = 0;
    while (!infile.eof() )
    {
        infile >> chemicalelement[count].atomicSymbol;
        infile >> chemicalelement[count].atomicNumber;
        infile >> chemicalelement[count].atomicMass;
        count++;
    }
    num = count;
    infile.close();
    return;
}//end readPeriodicTable

/* Function bubbleSort: recieves an array chemicalelement[], and sorts it in an
 * alphabetical order
 * Called by: main
 * Calles: none
 */
void bubbleSort(CElement chemicalelement[], int num)
{
    int j, pass;
    bool switched = true;
    CElement hold;
    for (pass = 0; pass < num - 1 && switched == true; pass++)
    {
        switched = false;
        for (j = 0; j < num - pass - 1; j++)
            if (chemicalelement[j].atomicSymbol > chemicalelement[j+1].atomicSymbol)
            {
                switched = true;
                hold = chemicalelement[j];
                chemicalelement[j]= chemicalelement[j+1];
                chemicalelement[j+1] = hold;
            }
    }
}// end bubbleSort
/* Function prinTable: recieves a sorted array chemicalelement[], and prints
 * neatly arranged table into a file output.txt
 * Called by: main
 * Calls: none
 */
void printTable(CElement chemicalelement[], int &num)
{
    ofstream outfile;
    outfile.open("output.txt");
    if(!outfile.is_open())
    {
        cout << endl << "ERROR; Unable to open file!" << endl;
        system("PAUSE");
        exit(1);
    }
    outfile << "Atomic Symbol    " << "Atomic Number    " << "Atomic Mass"
         << endl << endl;
    int count;
    for(count = 0; count < num; count++)
    {
        outfile.width(17);
        outfile << left << chemicalelement[count].atomicSymbol;
        outfile.width(17);
        outfile << left << chemicalelement[count].atomicNumber;
        outfile.width(17);
        outfile << left << chemicalelement[count].atomicMass << "\n";
    }
    return;
}// end printTable
void promptUser()
{
    cout << "Enter the molecular formula: "<< endl;
    cout << "Enter the weight in grams: " << endl;
}

float numberOfGramrsPerMole(CElement chemicalelement[], string molecularFormula)
{
    string s = molecularFormula, element1, element2;
    int subscript1, subscript2;
    
    for(int i = 0; i < s.length() ; i++) // not even close to solve the problem
    {
        if(s[i] == isupper()) 
        element1 = s[i];
        i++;
        else if(s[i] == isupper())
        element2 = s[i];
        subscript1 = 1;
    }
 
 
 
 
}