acos, acosf, acosl

Article
2017-12-18

The latest version of this topic can be found at acos, acosf, acosl.

Calculates the arccosine.

Syntax

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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