math.h问题 [英] Problems with math.h

问题描述

我正在编写一个使用math.h库中的函数sin()和cos()的程序.但是，我注意到我得到了时髦的结果.经过四处搜寻并检查过数学后，我决定使用以下方法进行简单检查:

I'm writing a program that is using the functions sin() and cos() from the math.h library. However, I noticed I was getting funky results. After searching around and checking my math multiple times, I decided to do a simple check with this:

int main()
{
    cout << "sin(45.0) = " << sin(45) << endl;
    cout << "cos(45.0) = " << cos(45) << endl;

    return 0;
}

我得到以下输出:

 sin(45) = 0.850904
 cos(45) = 0.525322

这些应该相等吧? math.h库有什么特别之处吗?我在做错什么吗?

These should be equal right? Is there something special about the math.h library? Am I doing something wrong?

以下是WolframAlpha中的方程式:

Here are the equations in WolframAlpha:

sin(45)

cos(45)

推荐答案

您应使用 cmath 在C ++中，而不是旧的C标头.

You should use cmath in C++, rather than the old C header.

std::sin() 和 此文件的GCC版本包含一个用于π(在C ++标准中不存在，但是)，这将使您更轻松地将度数转换为弧度:

The GCC version of this file includes a handy constant for π, (which does not exist in the C++ standard but) which will make it easier for you to convert degrees to radian:

#include <cmath>
#include <iostream>

double degrees_to_radian(double deg)
{
    return deg * M_PI / 180.0;
}

int main()
{
    std::cout << "sin(45.0) = " << std::sin(degrees_to_radian(45)) << std::endl;
    std::cout << "cos(45.0) = " << std::cos(degrees_to_radian(45)) << std::endl;
}

看到它运行！

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