calc

    double resolve(double op, double a, double b) {
        char s = static_cast<char> (op);
        switch (s) {
            case '+': return a + b;
            case '-': return a - b;
            case '/': return a / b;
            case '*': return a * b;
            case '^': return pow(a,b);
        }
    }

    double result() {
        stackClass s;
        double a, b;
        node tmp, r;
        while (!postfix.empty()) {
            tmp = postfix.pop();
            if (tmp.isOperator()) {
                b = s.pop().data;
                a = s.pop().data;
                r = node(resolve(tmp.data, a, b));
                s.push(r);
            } else {
                s.push(tmp);
            }
        }
        return s.pop().data;
    }