acos, acosf, acosl

Article
2015-04-28

Calculates the arccosine.

double acos( 
   double x 
);
float acos(
   float x 
);   // C++ only
long double acos(
   long double x
);   // C++ only
float acosf(
   float x 
);
long double acosl(
   long double x
);

Parameters

x
Value between –1 and 1, for which to calculate the arccosine (the inverse cosine).

Return Value

The acos function returns the arccosine of x in the range 0 to π radians.

By default, if x is less than –1 or greater than 1, acos returns an indefinite.

Input	SEH Exception	Matherr Exception
± ∞	INVALID	_DOMAIN
± QNAN,IND	none	_DOMAIN
\|x\|>1	INVALID	_DOMAIN

Remarks

Because C++ allows overloading, you can call overloads of acos that take and return float and long double types. In a C program, acos always takes and returns a double.

Requirements

Routine	Required header	Optional headers
acos, acosf, acosl	<math.h>	<errno.h>

Example

This program prompts for a value in the range -1 to 1. Input values outside this range produce _DOMAIN error messages. If a valid value is entered, the program prints the arcsine and the arccosine of that value.

// crt_asincos.c
// arguments: 0

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

int main( int ac, char* av[] )
{
    double  x,
            y;
    errno_t err; 

    // argument checking
    if (ac != 2)
    {
        fprintf_s( stderr, "Usage: %s <number between -1 and 1>\n",
                   av[0]);
        return 1;
    }

    // Convert argument into a double value
    if ((err = sscanf_s( av[1], "%lf", &x )) != 1)
    {
        fprintf_s( stderr, "Error converting argument into ",
                   "double value.\n");
        return 1;
    }

    // Arcsine of X
    y = asin( x );
    printf_s( "Arcsine of %f = %f\n", x, y );

    // Arccosine of X
    y = acos( x );
    printf_s( "Arccosine of %f = %f\n", x, y );
}

Arcsine of 0.000000 = 0.000000
Arccosine of 0.000000 = 1.570796

.NET Framework Equivalent

System::Math::Acos

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