C library functions -acos()

C standard library - <math.h>

Description

acos()is the C standard library<math.h>a function used to calculate the arccosine value of a number (also known as the cosine inverse function among inverse trigonometric functions).

acos()The function accepts a real number between -1 and 1 and returns the arccosine of that value, in radians.

Declaration

Below is the declaration of the acos() function.

#include <math.h>

double acos(double x);
float acosf(float x);
long double acosl(long double x);

Parameter

  • x-- a floating-point number between -1 and 1.

Return Value

  • returnxThe arccosine value, in radians. The range of the return value is [0, π].
  • ifxIf it is not within the range [-1, 1], the function will return NaN and set an appropriate math error (for example,EDOM）。

Example

The following example demonstrates the usage of the acos() function.

Example

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

int main() {
    double x = 0.5;
    double result = acos(x);

    printf("acos(%f) = %f radians\n", x, result);
    printf("acos(%f) = %f degrees\n", x, result * 180 / M_PI);

    return 0;
}

Code Analysis:

  • The code first includes the header file.<math.h>and<stdio.h>。
  • define a variablex, the value is 0.5.
  • Usageacos()Computexarc cosine value, and stores the result inresultIn.
  • printxthe arc cosine value, in radians.
  • Convert the result to degrees, and print it out. The conversion formula is:弧度 * (180 / π)。

Let us compile and run the above program, which will produce the following result:

acos(0.500000) = 1.047198 radians
acos(0.500000) = 60.000000 degrees

Error Handling

If the inputxexceeding the valid range [-1, 1],acos()will return NaN and seterrnoisEDOM. You can useisnan()The function checks whether the result is NaN:

Example

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

int main() {
    double x = 2.0;  // Invalid input, out of [-1, 1] range
    errno = 0;  // Reset errno
    double result = acos(x);

    if (errno == EDOM) {
        printf("Input value is out of domain. acos(%f) is not defined.\n", x);
    } else {
        printf("acos(%f) = %f radians\n", x, result);
    }

    return 0;
}

Code Analysis:

  • The code attempts to calculateacos(2.0), this is an invalid input, because 2.0 is not within the range [-1, 1].
  • errnois reset to 0, then callacos(x)。
  • CheckserrnoWhether it equalsEDOM, if so, print an error message.
  • If there are no errors, the calculation result is printed.

Let us compile and run the above program, which will produce the following result:

acos(2.000000) = nan radians

acos()The function is used to calculate the arc cosine of a given value, and is a common tool for handling inverse trigonometric operations. When using it, ensure that the input value is within the range [-1, 1], and handle possible error conditions. By converting the result to degrees, the result can be understood more intuitively.

C standard library - <math.h>

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