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# acos, acosf

Visual Studio .NET 2003

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
);
```

#### Parameter

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

#### Return Value

The acos function returns the arccosine of x in the range 0 to &pi; radians.

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

Input SEH Exception Matherr Exception
± &infin; INVALID _DOMAIN
± QNAN,IND none _DOMAIN
|x|>1 INVALID _DOMAIN

#### Remarks

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

#### Requirements

acos, acosf <math.h> <errno.h> ANSI, Win 98, Win Me, Win NT, Win 2000, Win XP

For additional compatibility information, see Compatibility in the Introduction.

Libraries

All versions of the C run-time libraries.

#### Example

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;

if (ac != 2) {
fprintf(stderr, "Usage: %s <number between -1 and 1>\n", av[0]);
return 1;
}
sscanf( av[1], "%lf", &x );
y = asin( x );
printf( "Arcsine of %f = %f\n", x, y );
y = acos( x );
printf( "Arccosine of %f = %f\n", x, y );
}
```

#### Output

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