我在使用面向 object 的编程时遇到问题

Question

I'm having problem in my programming classes, basically we're learning about object oriented programming and I'm building a program, this is a part of the code:

float Pedido::calculaTotal() const {
    std::list<Produto*>::const_iterator it;
    float valorTotal;
    for (it = m_produtos.begin(); it != m_produtos.end(); ++it){
        int quantidade = it->getQtd();
        float valor = it->getValor();
        valorTotal += quantidade * valor;
    }
  return 0;
}

I"m getting this error:

---

pedido.cpp: In member function 'float Pedido::calculaTotal() const': pedido.cpp:20:30: error: request for member 'getQtd' in '* it.std::_List_const_iterator<Produto*>::operator->()', which is of pointer type 'Produto* const' (maybe you meant to use '->'?) int quantidade = it->getQtd(); ^~~~~~

pedido.cpp:21:27: error: request for member 'getValor' in '* it.std::_List_const_iterator<Produto*>::operator->()', which is of pointer type 'Produto* const' (maybe you meant to use '->'?) float valor = it->getValor();

---

Answer 1

Tudo bem Fabricio? Your program is almost correct, you just need a couple of corrections. You need to initialize total to zero and then return it in the end.

float Pedido::calculaTotal() const {
    std::list<Produto*>::const_iterator it;
    float valorTotal = 0;
    for (it = m_produtos.begin(); it != m_produtos.end(); ++it){
        Produto* p = *it;
        int quantidade = p->getQtd();
        float valor = p->getValor();
        valorTotal += quantidade * valor;
    }
  return valorTotal;
}

Also the iterator is a "pointer" itself so *it has the type of Produto* and to get the actual Produto object you need to dereference twice with either (*it)-> or alternatively do what I did above, get the pointer with Produto* p = *it; then use the actual pointer with p-> .

Alternatively you can also use ranges like this:

float Pedido::calculaTotal() const {
    float valorTotal = 0;
    for ( Produto* p : m_produtos ) {
        valorTotal += p->getQtd() * p->getValor();
    }
    return valorTotal;
}