Question

首先，我想说我是C ++的新手。我一直在从网站上学习，尝试花费数小时改写我的代码，并尝试新事物以尝试解决此问题。

当我在修改变量的函数中引用变量时，它将返回正确的值。离开该函数后，即使我已将变量传递给下一个函数，也将重置这些值。我什至在这里和那里添加了cout来显示值以帮助我调试，但是没有任何结果。有人可以指出我正确的方向吗？我将在下面发布我的代码。谢谢大家的帮助。

#include <iostream>

//void Loop(int Total, int Spend);
//int NewTotal(int Total, int Spend);
//void Spent(int Total, int Spend);
void UserInput(int Total, int Spend);

// Loops back to UserInput() for next entry input
void Loop(int Total, int Spend)
{
    UserInput(Total, Spend);
}

int NewTotal(int Total, int Spend)
{
    std::cout << "Output of Total is: " << Total << std::endl;
    std::cout << "Output of Spend is: " << Spend << std::endl;
    return Total + Spend;
}

void Expense()
{
    std::cout << "Please enter a description of your expense!" << std::endl;
    char ExpenseDesc;
    std::cin >> ExpenseDesc;
    std::cout << "You described your expense as: " << std::endl;
    std::cout << ExpenseDesc << std::endl;
}

void Spent(int Total, int Spend)
{
    std::cout << "Please enter the amount you spent!" << std::endl;
    std::cin >> Spend;
    NewTotal(Total, Spend);
}

void UserInput(int Total, int Spend)
{
    Expense();
    Spent(Total, Spend);
    std::cout << "Result of Total and Spend (NewTotal) is: " << Total + Spend << std::endl;
    std::cout << "Record saved!" << std::endl;
    std::cout << "So far, you have spent " << NewTotal(Total, Spend) << "!" << std::endl; //int Total & int Spend not retaining value when NewTotal(Total, Spend) gets called again to return value
    std::cout << "Ready for next entry!" << std::endl;
    Loop(Total, Spend);
}

int main()
{
    int Total;
    int Spend; 
    Spend = 0;
    Total = 0;
    UserInput(Total, Spend);
    return 0;
}

从本质上讲，这是一个非常基本的提示，要求您提供交易说明（该交易只接受一个字符，我需要解决此问题）和交易金额。完成输入后，您可以再输入一次，该程序应该将旧的总计添加到新的总计中，以得出到目前为止的总支出，然后重复提示。

Answer 1

您需要通过引用传递变量或从函数中返回它们。就目前而言，您将创建每个函数本地的每个变量的副本，修改副本，然后在范围末尾将其丢弃。

返回值：

std::pair<int, int> Spent(int Total, int Spend) {
    ...
    return std::make_pair(Total, Spend);
}

// Getting values out
std::pair<int, int> result = Spent(Total, Spend);
int newTotal = result.first;
int newSpend = result.second;
// or
int newTotal, newSpend;
std::tie(newTotal, newSpend) = Spent(Total, Spend);
// or (C++17)
auto [newTotal, newSpend] = Spent(Total, Spend);

参考参数：

void Spent(int& Total, int& Spend) {
    // Modifications to Total and Spend in this function will apply to the originals, not copies
    ...
}

Answer 2

另一种选择是传递指针：

[dismissable]="true/false"

或使用std :: tuple：

void f(int* Total, int* Spent)
{
    *Total = ...;
    *Spent = ...;
}

即使我通过作用域传递变量，也无法访问变量的值

2 个答案: