# acos, acosf, acosl

Calculates the arccosine.

## Syntax

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

### 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

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
``````