Usage and example of C library function acos()

C Standard Library <math.h>

The acos() function returns the arccosine value represented by a number in radians.

The acos() function takes a single parameter (1≥x≥-1）and returns the arccosine value in radians.

The acos() function is included in the <math.h> header file.

The prototype of acos() function

double acos(double x);

To find the inverse cosine for types int, float, or long double, you can use the type cast operator to explicitly convert the type to double.

　int x = 0;
　double result;
　result = acos(double(x));

Additionally, C99Two functions acosf() and acosl() were introduced in C

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

acos() parameters

The acos() function uses [-1,+1This is because the cosine value is1] range.-1to

acos() return value

The acos() function returns a value in the range [0.0, π] in radians units. If the parameter passed to the acos() function is less than-1or greater1If the parameter is less than or greater than

Example1: acos() function with different parameters

#include <stdio.h>
#include <math.h>
int main()
{
　　　　//Defined constant PI
　　　　const double PI =　　3.1415926;
　　　　double x, result;
　　　　x =　　-0.5;
　　　　result = acos(x);
　　　　printf("cos(%.2f) Inverse cosine value = %.2lf radians\n", x, result);
　　　　//Convert radians to degrees
　　　　result = acos(x)*180/PI;
　　　　printf("cos(%.2f) Inverse cosine value = %.2lf degree\n", x, result);
　　　　//Parameter is out of range
　　　　x =　1.2;
　　　　result = acos(x);
　　　　printf("Inverse of cos(%.2f) = %.2lf", x, result);
　　　　return 0;
{}

Output Result

cos(-0.50) Inverse cosine value =　2.09　radians
cos(-0.50) Inverse cosine value =　120.00 degrees
cos(1.20) Inverse cosine value = nan

Example2: acosf() and acosl() functions

#include <stdio.h>
#include <math.h>
int main()
{
　　　　float fx, facosx;
　　　　long double lx, ldacosx;
　　　　//Floating point inverse cosine
　　　　fx =　-0.505405;
　　　　facosx = acosf(fx);
　　　　//Long double type inverse cosine
　　　　lx =　-0.50540593;
　　　　ldacosx = acosf(lx);
　　　　printf("acosf(x) = %f radians\n", facosx);
　　　　printf("acosl(x) = %Lf radians", ldacosx);
　　　　return 0;
{}

Output Result

acosf(x) =　2.100648　radians
acosl(x) =　2.100649　radians

C Standard Library <math.h>