c++ - 运行时错误 #3

Question

我正在学习 C++ 类(class)，我们正在使用 visual studio。我们的任务是创建一个程序来计算不同的东西，用户可以通过输入相应的字符来选择这些东西。该事件旨在向我们展示如何在代码中使用函数。我已经设置了第一个计算，但每次运行它时，我都会收到运行时错误 #3，当我在主程序中初始化 circleArea 时，circleArea 将打印为我初始化它的值，而不是 areaCircle 函数返回的值。谢谢你帮我解决问题，如果这对我来说是非常初级的，我很抱歉。

---

/// Lab6Marcelino.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
#include <string>
#include <iomanip>
using namespace std;

double pi = 3.14;

// Protoypes
void showMenu(char & c);
void getRadius(double & r, bool &nega);
bool isNegative(double val);
double areaCircle(double &r);

// Main
int _tmain(int argc, _TCHAR* argv[])
{
    char menuChoice;
    double radius;
    bool negative = true;
    double circleArea;

    showMenu(menuChoice);

    if (menuChoice = 'c')
    {
        getRadius(radius, negative);
        areaCircle(radius);

        cout << "The radius is " << radius << endl
            << "The area of the circle is: " << circleArea << endl;
    }



    system("Pause");
    return 0;
}

//*************
// FUNCTIONS***
//*************

// Definition of function showMenu
// Shows Menu and asks for user choice.

void showMenu(char &menuChoice)
    {
        cout << "Enter C or c for the area of a Circle" << endl
        << "Enter T or t for the area of a Triangle" << endl
        << "Enter S or s for the area of a Sphere" << endl
        << "Enter P or p for the area of a triangular Prism" << endl
        << "Enter A or a for information about the author" << endl
        << "Enter Q or q to quit this program" << endl;
        cin >> menuChoice;
    }

// Definition of function getRadius
// Gets radius from user

void getRadius(double &r, bool &nega)
    {
        cout << "Enter the radius: ";
    cin >> r;
        isNegative(r);

        while (isNegative(r) == true)
        {
            cout << "Enter the radius: ";
            cin >> r;
            isNegative(r);
        }
    }

bool isNegative(double val)
    {
        if (val < 0)
            return true;

        if (val > 0)
            return false;
        else
        {
            cout << "Invalid input" << endl;
            return true;
        }
    }

double areaCircle(double &r)
{
    double circleArea;
    circleArea = pi * r * r;
    return circleArea;
}

Answer 1

areaCircle(radius); 返回一个值，但您没有将它分配给任何东西。然后，当您尝试将 circleArea 与 cout 一起使用时，它尚未初始化，所以这可能是您遇到运行时错误的地方。