c中tan（90）的值？

它给出的值是557135813.94455。值是否每次都保持不变？？为什么它不显示无限

#include <stdio.h>     
#include <math.h>       

#define PI 3.14159265

int main ()
{
  double param, result;
  param = 90.0;
  result = tan ( param * PI / 180.0 );
  printf ("The tangent of %f degrees is %f.\n", param, result );
  return 0;
}

#包括
#包括
#定义PI 3.14159265
int main（）
{
双参数，结果；
参数=90.0；
结果=tan（参数*PI/180.0）；
printf（“%f度的切线为%f.\n”，参数，结果）；
返回0；
}

您没有传递Pi/2的值，而是传递90.0*3.14159265/180.0的近似值。

浮点算术不是精确的算术。您甚至不能使用

==

比较两个浮点数；e、 g.

0.6/0.2-3==0

应为真，但在大多数系统上为假。在执行浮点计算和期望精确结果时要小心；这是注定要失败的。考虑每个浮点计算只返回一个近似值；尽管这是一个非常好的值，有时甚至是一个精确值，但不要依赖它来精确。

代码要求的不是90°的切线，而是一个数字的切线，以弧度表示，接近90°。弧度的转换并不精确，因为π/2弧度不能精确表示为

double

解决方案是首先执行度数范围缩减，然后调用

tan（d2r（x））

更好的结果

The tangent method 1 of -360.0 degrees is  -2.4492935982947064e-16
The tangent method 2 of -360.0 degrees is  0.0000000000000000e+00
The tangent method 1 of -330.0 degrees is  -5.7735026918962640e-01
The tangent method 2 of -330.0 degrees is  -5.7735026918962573e-01
The tangent method 1 of -300.0 degrees is  -1.7320508075688770e+00
The tangent method 2 of -300.0 degrees is  -1.7320508075688774e+00
The tangent method 1 of -270.0 degrees is  5.4437464510651230e+15
The tangent method 2 of -270.0 degrees is  -inf
The tangent method 1 of -240.0 degrees is  1.7320508075688752e+00
The tangent method 2 of -240.0 degrees is  1.7320508075688774e+00
The tangent method 1 of -210.0 degrees is  5.7735026918962540e-01
The tangent method 2 of -210.0 degrees is  5.7735026918962573e-01
The tangent method 1 of -180.0 degrees is  -1.2246467991473532e-16
The tangent method 2 of -180.0 degrees is  0.0000000000000000e+00
...

---

阅读关于度、辐射等的

90.0*pi/180.0

非常令人困惑。为什么不干脆

pi/2

？编辑：Nevermind甚至没有注意到这是一个度到弧度的转换。不要自己定义圆周率，使用math.hOn我的系统中的M_PI、M_PI或M_PIl。你的程序的输出是557135115.020977。@nsilent22

M_PI

不是标准的

请参见

Angle  1.5707963250000001e+00 radian
Pi/2 = 1.5707963267948966192313216916398...
The tangent of 90.000000 degrees is 557135183.943528.

The tangent method 1 of -360.0 degrees is  -2.4492935982947064e-16
The tangent method 2 of -360.0 degrees is  0.0000000000000000e+00
The tangent method 1 of -330.0 degrees is  -5.7735026918962640e-01
The tangent method 2 of -330.0 degrees is  -5.7735026918962573e-01
The tangent method 1 of -300.0 degrees is  -1.7320508075688770e+00
The tangent method 2 of -300.0 degrees is  -1.7320508075688774e+00
The tangent method 1 of -270.0 degrees is  5.4437464510651230e+15
The tangent method 2 of -270.0 degrees is  -inf
The tangent method 1 of -240.0 degrees is  1.7320508075688752e+00
The tangent method 2 of -240.0 degrees is  1.7320508075688774e+00
The tangent method 1 of -210.0 degrees is  5.7735026918962540e-01
The tangent method 2 of -210.0 degrees is  5.7735026918962573e-01
The tangent method 1 of -180.0 degrees is  -1.2246467991473532e-16
The tangent method 2 of -180.0 degrees is  0.0000000000000000e+00
...