由于变量是本地而不是全局而导致的运行时错误

Question

以下代码要求用户选择一个形状，输入该形状的尺寸，并显示其体积。

当我运行代码时，我得到以下输出，显示结果不是数字（NaN）：

我意识到这一定与我的变量是局部变量而不是全局变量以及以下函数调用有关：

choice = ReadInputShapeChoice();
readshapedimension(choice);
result = CalculateBasicVolume(choice);

没有传递所需的数据。已尝试解决此问题并将变量放在正确的位置但无济于事，我是使用任何形式的编码语言的初学者，发现整个程序的创建相当具有挑战性。

我已经发布了一个类似的问题，但是这个问题要详细得多，如果有人能阐明我如何修改变量的位置以使程序正确运行，我将不胜感激。谢谢。

完整代码为：

#include <iostream>
using namespace std;

double height, width, length, radius, base_area, result;

 //Function prototypes

int ReadInputShapeChoice();
void readshapedimension(int choice);
float CalculateBasicVolume(int choice);
void PrintResult(int choice);

double rectangular_solid(double length1, double width1, double height1);
double cylinder(double radius2, double height2);
double cone(double radius3, double height3);
double sphere(double radius4);
double square_based_pyramid(double height5, double base_area5);

//function definitions
double rectangular_solid(double length1, double width1, double height1)
{
    double value;
    value = (length1 * width1 * height1);
    return value;
}
double cylinder(double radius2, double height2)
{
    double value;
    value = (3.14159 * (radius2 * radius2) * height2);
    return value;
}
double cone(double radius3, double height3)
{
    double value;
    value = ((3.14159 * (radius3 * radius3) * height3) / 3);
    return value;
}
double sphere(double radius4)
{
   double value;
   value = ((3.14159 * (radius4 * radius4 * radius4))*(4 / 3));
   return value;
}
double square_based_pyramid(double height5, double base_area5)
   {
   double value;
   value = ((height5 * base_area5) * (1 / 3));
   return value;
   }


int ReadInputShapeChoice()
{   int choice;
    cout << "Choose what shape you want to calculate" << endl;
    cout << "1 = Rectangular solid" << endl;
    cout << "2 = Cylinder" << endl;
    cout << "3 = Cone" << endl;
    cout << "4 = Sphere" << endl;
    cout << "5 = Square based pyramid" << endl;
    cin >> choice;
    return choice;
}

void readshapedimension(int choice)
{
    switch (choice)
    {
    case 1:
    {
        int length, width, height;
        cout << "You have chosen rectuangular solid" << endl;
        cout << "Enter the values for length width and height" << endl;
        cin >> length >> width >> height;
        break;
    }
    case 2:
    {
        int radius, height;
        cout << "You have chosen cylinder" << endl;
        cout << "Enter the values for radius and height" << endl;
        cin >> radius >> height;
        break;
    }
    case 3:
    {
        int radius, height;
        cout << "You have chosen cone" << endl;
        cout << "Enter the values for radius and height" << endl;
        cin >> radius >> height;
        break;
    }
    case 4:
    {
        int radius;
        cout << "You have chosen sphere" << endl;
        cout << "Enter the radius" << endl;
        cin >> radius;
        break;
    }
    case 5:
    {
        int height, base_area;
        cout << "You have chosen square based pyramid" << endl;
        cout << "Enter height and area of the base" << endl;
        cin >> height >> base_area;
        break;
    }
    }
}

float CalculateBasicVolume(int choice)
{
switch (choice)
{
    int result;
case 1:
{
    result = rectangular_solid(length, width, height);
    break;
}
case 2:
{
    result = cylinder(radius, height);
    break;
}
case 3:
{
    result = cone(radius, height);
    break;
}
case 4:
{
    result = sphere(radius);
    break;
}
case 5:
{
    result = square_based_pyramid(height, base_area);
    break;
}
    return result;
    }
}
void PrintResult(int choice)
{
    switch (choice)
    {
case 1:
{
    cout << "The volume of the rectangular solid is " << result << endl;
    break;
}
case 2:
{
    cout << "the volume of the cylinder is " << result << endl;
    break;
}
case 3:
{
    cout << "The volume of the cone is " << result << endl;
    break;
}
case 4:
{
    cout << "The volume of the sphere is " << result << endl;
    break;
}
case 5:
{
    cout << "the volume of the square based pyramid is " << result <<     endl;
    break;
}

}
}



int main() {
    int choice;
    choice = ReadInputShapeChoice();
    readshapedimension(choice);
    result = CalculateBasicVolume(choice);
    PrintResult(choice);

        return 0;
}}

Answer 1

你在你的函数中重新声明；这会导致函数使用它们的局部值而不是全局值，例如，我在您的 reshapedimensions 函数中注释掉了重新声明：

// This is our global declaration
double height, width, length, radius, base_area, result;

void readshapedimension(int choice)
{
    switch (choice)
    {
    case 1:
    {
        // Take out our local declarations
        // Otherwise cin below will write to the local and these values
        // will subsequently be lost when the function exits
        //int length, width, height;
        cout << "You have chosen rectuangular solid" << endl;
        cout << "Enter the values for length width and height" << endl;
        cin >> length >> width >> height;
        break;
    }
    case 2:
    {
        //int radius, height;
        cout << "You have chosen cylinder" << endl;
        cout << "Enter the values for radius and height" << endl;
        cin >> radius >> height;
        break;
    }
    case 3:
    {
        //int radius, height;
        cout << "You have chosen cone" << endl;
        cout << "Enter the values for radius and height" << endl;
        cin >> radius >> height;
        break;
    }
    case 4:
    {
        //int radius;
        cout << "You have chosen sphere" << endl;
        cout << "Enter the radius" << endl;
        cin >> radius;
        break;
    }
    case 5:
    {
        //int height, base_area;
        cout << "You have chosen square based pyramid" << endl;
        cout << "Enter height and area of the base" << endl;
        cin >> height >> base_area;
        break;
    }
    }
}

不过，我注意到您在函数中使用了int，在全局声明中使用了double；如果这是故意的，您需要在某处包含转换并将结果存储回全局变量。

保持全局名称的唯一性是个好主意，这样您就不会将它们与本地名称混淆；常见的技术是使用ALLCAPS 或glob_myvar 等前缀。

Answer 2

您正在重新定义 result 变量。

在文件的顶部声明它；

double result;

但你从不初始化它，而是稍后重新定义它并将你想要打印的值放入这个新变量中；

float CalculateBasicVolume(int choice)
{
    switch (choice)
    {
        int result;

您稍后打印的变量是未初始化的 double，而不是实际包含圆锥体积的 int。