# acos, acosf, acosl

Visual Studio 2013

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

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```