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# acos, acosf

Visual Studio 2005

Calculate the arccosine.

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

#### Parameters

x

Value between –1 and 1 whose arccosine is to be calculated.

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

If x is less than –1 or greater than 1, acos returns an indefinite by default.

Input SEH Exception Matherr Exception

± ∞

INVALID

_DOMAIN

± QNAN,IND

none

_DOMAIN

|x|>1

INVALID

_DOMAIN

C++ allows overloading, so you can call overloads of acos. In a C program, acos always takes and returns a double.

acos, acosf

<math.h>

<errno.h>

ANSI, Windows 95, Windows 98, Windows 98 Second Edition, Windows Millennium Edition, Windows NT 4.0, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003

This program prompts for a value in the range -1 to 1. Input values outside this range will 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 );
}
```

#### Output

```Arcsine of 0.000000 = 0.000000
Arccosine of 0.000000 = 1.570796```