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acos, acosf 

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 



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

± ∞









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

Routine Required header Optional headers Compatibility

acos, acosf



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,
    errno_t err; 

    // argument checking
    if (ac != 2)
        fprintf_s( stderr, "Usage: %s <number between -1 and 1>\n",
        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