#include <ctype.h>    // Provides isdigit
#include <iostream.h> // Provides cout, cin, peek, ignore
#include <string.h>   // Provides strchr
#include "stack2.h"   // Provides the Stack template class

void evaluate_stack_tops(Stack<double>& numbers, Stack<char>& operations)
{
    double operand1, operand2;

    operand2 = numbers.pop( );
    operand1 = numbers.pop( );
    switch (operations.pop( ))
    {
        case '+': numbers.push(operand1 + operand2);
                  break;
        case '-': numbers.push(operand1 - operand2);
                  break;
        case '*': numbers.push(operand1 * operand2);
                  break;
        case '/': numbers.push(operand1 / operand2);
                  break;
    }
}

double read_and_evaluate(istream& ins)
{
    const char DECIMAL = '.';
    const char RIGHT_PARENTHESIS = ')';

    Stack<double> numbers;
    Stack<char> operations;
    double number;
    char symbol;
    
    while (!ins.eof( ) && ins.peek( ) != '\n')
    {
        if (isdigit(ins.peek( )) || (ins.peek( ) == DECIMAL))
        {
            ins >> number;
            numbers.push(number);
        }
        else if (strchr("+-*/", ins.peek( )) != NULL)
        {
            ins >> symbol;
            operations.push(symbol);
        }
        else if (ins.peek( ) == RIGHT_PARENTHESIS)
        {
            cin.ignore( );
            evaluate_stack_tops(numbers, operations);
        }
        else
            cin.ignore( );
    }
    return numbers.pop( );
}



void main( )
{   double answer;
    cout << "Type a fully parenthesized arithmetic expression:" << endl;
    answer = read_and_evaluate(cin);
    cout << "That evaluates to " << answer << endl;
}