初学者在 C++ 中调用函数，代码编译数学是错误的

Posted 2023-04-14

【中文标题】初学者在 C++ 中调用函数，代码编译数学是错误的

【英文标题】：beginner calling functions in c++, code compiles math is wrong

【发布时间】：2021-04-19 04:45:53

【问题描述】：

所以我是 C++ 新手，我认为我了解如何在函数方面掌握基础知识，但我遇到了一些问题。在作业中，我需要返回值距离、半径、周长、面积和直径。当前使用代码块，代码编译但不能正常工作。任何帮助表示赞赏！

#include <iostream>
#include <cmath>
#include <iomanip>
#include <cctype>

using namespace std;
double const PI = 3.1416;//constant global variable
double distance(double, double, double, double);//prototype for distance function after main
double radius (double, double, double, double, double);//prototype for radius after main
double circumference(double);//prototype for circumference after main
double area(double);//prototype for area after main
int main()

    double x1, y1, x2, y2;
    cout << fixed << showpoint << setprecision(2);
    cout << "Enter the center X and Y coordinate of a circle (in that order with a space in between): ";
    cin >> x1 >> y1;//center coordinates
    cout << "Enter another X and Y coordinate in the same circle (in that order with a space in between): ";
    cin >> x2 >> y2; // second set of coordinates
    cout << "Circle's radius is: " << radius << endl;
    cout << "Circle's circumference is: " << circumference << endl;
    cout << "Circle's area is: " << area << endl;
    double diameter = 2*radius(x1, y1, x2, y2, distance(x1, y1, x2, y2));
    cout << "Circle's diameter is: " << diameter << endl;
    return 0;
//end main
double distance(double x1, double y1, double x2, double y2)

    double distance = sqrt(pow(x2-x1,2) + pow(y2-y1,2));
    return distance;
//end distance
double radius(double x1, double y1, double x2, double y2, double distance)

    double radius = distance;
    return radius;
//end radius
double circumference(double radius)

    double circumference = 2*PI*radius;
    return circumference;
//end circumference
double area(double radius)

   double area = pow(PI*radius,2);
   return area;
//end area

【问题讨论】：

您使用的输入是什么？预期和实际输出是多少？您可能打算调用这些函数并使用返回值 cout << "Circle's radius is: " << radius << endl; -> cout << "Circle's radius is: " << radius(...) << endl;

我的输入主要来自用户。我要求一个中心坐标和另一个坐标，都在一个圆圈中。尽管你怎么说，这更有意义。非常感谢。我仍在积极努力。

【参考方案1】：

我修复了你的代码：

#include <iostream>
#include <cmath>
#include <iomanip>
#include <cctype>
using namespace std;
double const PI = 3.1416;//constant global variable
double distance(double, double, double, double);//prototype for distance function after main
double radius (double, double, double, double, double);//prototype for radius after main
double circumference(double);//prototype for circumference after main
double area(double);//prototype for area after main
int main()

    double x1, y1, x2, y2;
    cout << fixed << showpoint << setprecision(2);
    cout << "Enter the center X and Y coordinate of a circle (in that order with a space in between): ";
    cin >> x1 >> y1;//center coordinates
    cout << "Enter another X and Y coordinate in the same circle (in that order with a space in between): ";
    cin >> x2 >> y2; // second set of coordinates
    cout << "Circle's radius is: " << radius << endl;
    cout << "Circle's circumference is: " << circumference << endl;
    cout << "Circle's area is: " << area << endl;
    double diameter = 2*radius(x1, y1, x2, y2, distance(x1, y1, x2, y2));
    cout << "Circle's diameter is: " << diameter << endl;
    return 0;
//end main
double distance(double x1, double y1, double x2, double y2)

    double distance = sqrt(pow(x2-x1,2) + pow(y2-y1,2));
    return distance;
//end distance
double radius(double x1, double y1, double x2, double y2, double distance)

    double radius = distance;
    return radius;
//end radius
double circumference(double radius)

    double circumference = 2*PI*radius;
    return circumference;
//end circumference
double area(double radius)

   double area = pow(PI*radius,2);
   return area;
//end area

你的代码有很多问题：

未正确调用函数

考虑一下你写的这些行：

cout << "Circle's radius is: " << radius << endl;
cout << "Circle's circumference is: " << circumference << endl;
cout << "Circle's area is: " << area << endl;

这里的问题是你没有按照他们应该的方式调用函数。您在代码末尾定义了函数，并将一些函数分别命名为半径、周长和面积。这里的问题是，当您尝试调用该函数时，您没有将参数发送到您的函数中，这就是为什么它不会产生正确的结果。您必须按照函数定义/原型中提到的相同顺序传递适当的参数，以便将值传递给您的函数以产生所需的结果。

数学错误

考虑一下你写的这些行：

double area(double radius)

   double area = pow(PI*radius,2);
   return area;

圆的面积 = π x r^2

pow(PI*radius,2) 

将返回一个等于 (π x r)^2 的值，因此在使用数学函数时要小心。

使用正确的编程实践

我不会将其视为您的代码中的问题，但如果您学会编写高效的代码，它将使您的编码之旅更加轻松。你学得越多，你就会发现使用它们的重要性，因为在这些基本问题上的差异几乎可以忽略不计。

考虑一下我要为这个问题编写的代码：

#include <iostream>
#include <cmath>
#include <iomanip>
#include <cctype>
using namespace std;

double const PI = 3.1416;//constant global variable
double distance(double, double, double, double);//prototype for distance function after main
double radius (double, double, double, double);//prototype for radius after main
double circumference(double);//prototype for circumference after main
double area(double);//prototype for area after main

int main()

    double x1, y1, x2, y2;
    cout << "Enter the center X and Y coordinate of a circle (in that order with a space in between): "<<endl;
    cin >> x1 >> y1;//coordinates of point 1
    cout << "Enter another X and Y coordinate in the same circle (in that order with a space in between): "<<endl;
    cin >> x2 >> y2; // second set of point 2
    cout << "Circle's radius is: " << radius(x1,y1,x2,y2) << endl;
    cout << "Circle's circumference is: " << circumference(radius(x1,y1,x2,y2)) << endl;
    cout << "Circle's area is: " << area(radius(x1,y1,x2,y2)) << endl;
    cout << "Circle's diameter is: " << 2 * radius(x1, y1, x2, y2) << endl;
    return 0;
//end main

double distance(double x1, double y1, double x2, double y2)

    double distance = sqrt(pow(x2-x1,2) + pow(y2-y1,2));
    return distance;
//end distance
double radius(double x1, double y1, double x2, double y2)

    double radius = distance(x1,y1,x2,y2)/2;
    return radius;
//end radius
double circumference(double radius)

    double circumference = 2*PI*radius;
    return circumference;
//end circumference
double area(double radius)

   double area = PI * pow(radius,2);
   return area;
//end area

在初学者级别我会说你做得很好：D

查看主题并返回此问题以更好地理解该主题。此外，请记住，如果您想擅长编程，练习是关键。所以，拥抱磨砺吧。

编码愉快！

【讨论】：

非常感谢您对我的问题的详尽解释。这对我帮助很大。还。非常感谢您用我的面积表达式发现数学错误。我正在尽力掌握这个概念。当我大声说出来时，我可以做到，付诸实践是我滑倒并感到迷茫的地方！虽然你的崩溃有很大帮助！谢谢你，我希望你有一个美好的一天

没问题老兄！ :) 乐于助人。

【参考方案2】：

您遇到的问题是，在 C++ 中调用函数时，它必须采用 foo(bar) 格式，其中 bar 代表函数的输入参数。例如，在您的原型中，您使用 5 个参数定义半径，但是当您稍后调用它时，它没有要评估的参数。也许对 C++ 有更多了解的人可以回答为什么在 cout 中调用 radius 会导致返回值 1 但是我相信这个值是程序尝试执行调用时返回的退出代码。在这种情况下，调用 radius 或任何函数的正确方法是为其提供适当数量的参数，这些参数被定义为接收，即 radius(x1, y1, x2, y2)。

我还注意到一些事情，area() 中计算圆面积的语句不正确，您希望 PI*pow(radius,2) 因为它当前的方式是首先计算 PI*radius，然后再计算结果是平方的。另一件事是，在半径中，您已将距离声明为参数，当我认为您打算从半径函数中调用距离时必须填充该参数，因此可以从半径的原型和实现中删除。附件是您的代码，其中包含为纠正问题而进行的细微调整。

#include <iostream>
#include <cmath>
#include <iomanip>
#include <cctype>

using namespace std;
double const PI = 3.1416;//constant global variable
double distance(double, double, double, double);//prototype for distance function after main
double radius (double, double, double, double);//prototype for radius after main
double circumference(double);//prototype for circumference after main
double area(double);//prototype for area after main
int main()

    double x1, y1, x2, y2;
    cout << fixed << showpoint << setprecision(2);
    cout << "Enter the center X and Y coordinate of a circle (in that order with a space in between): ";
    cin >> x1 >> y1;//center coordinates
    cout << "Enter another X and Y coordinate in the same circle (in that order with a space in between): ";
    cin >> x2 >> y2; // second set of coordinates
    cout << "Circle's radius is: " << radius(x1,y1,x2,y2) << endl;
    cout << "Circle's circumference is: " << circumference(radius(x1,y1,x2,y2)) << endl;
    cout << "Circle's area is: " << area(radius(x1,y1,x2,y2)) << endl;
    double diameter = 2*radius(x1, y1, x2, y2);
    cout << "Circle's diameter is: " << diameter << endl;
    return 0;
//end main
double distance(double x1, double y1, double x2, double y2)

    double distance = sqrt(pow(x2-x1,2) + pow(y2-y1,2));
    return distance;
//end distance
double radius(double x1, double y1, double x2, double y2)

    double radius = distance(x1, y1, x2, y2);
    return radius;
//end radius
double circumference(double radius)

    double circumference = 2*PI*radius;
    return circumference;
//end circumference
double area(double radius)

   double area = PI*pow(radius,2);
   return area;
//end area

【讨论】：

非常感谢您帮助我并指出一些问题。我已经通读了这些 cmets，并且也在积极研究我的代码。以确保我在实践中完全掌握这些概念。我非常感谢你们所有人。谢谢 :] 祝你有美好的一天！

【参考方案3】：

所以我能够对其进行返工，并且我对将函数调用付诸实践有了更多的了解！我修正了数学并在 main 中为半径创建了一个变量，这样我可以更有效地调用它！我也稍微调整了功能。我对定义有点迷失了哈哈。谢谢大家的帮助！

#include <iostream>
#include <cmath>
#include <iomanip>
#include <cctype>

using namespace std;
//Part 1 - circle
double const PI = 3.1416;//constant global variable
double distance(double, double, double, double);//prototype for distance function after main
double radius (double, double, double, double);//prototype for radius after main
double circumference(double);//prototype for circumference after main
double area(double);//prototype for area after main
int main()

    double x1, y1, x2, y2;
    cout << fixed << showpoint << setprecision(2);
    cout << "Enter the center X and Y coordinate of a circle (in that order with a space in between): ";
    cin >> x1 >> y1;//center coordinates
    cout << "Enter another X and Y coordinate in the same circle (in that order with a space in between): ";
    cin >> x2 >> y2; // second set of coordinates
    double r = radius(x1, y1, x2, y2);
    cout << "Circle's radius is: " << r << endl;
    cout << "Circle's circumference is: " << circumference(r) << endl;
    cout << "Circle's area is: " << area(r) << endl;
    double diameter = 2*r;
    cout << "Circle's diameter is: " << diameter << endl;
    return 0;
//end main
double distance(double x1, double y1, double x2, double y2)

    double distance = sqrt(pow(x2-x1,2) + pow(y2-y1,2));
    return distance;
//end distance
double radius(double x1, double y1, double x2, double y2)

    double radius = distance(x1, y1, x2, y2);
    return radius;
//end radius
double circumference(double radius)

    double circumference = 2*PI*radius;
    return circumference;
//end circumference
double area(double radius)

   double area = PI*pow(radius,2);
   return area;
//end area