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acos, acosf, acosl


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

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  


Value between –1 and 1, for which to calculate the arccosine (the inverse cosine).

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.

InputSEH ExceptionMatherr Exception

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.

RoutineRequired headerOptional headers
acos, acosf, acosl<math.h><errno.h>

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,  
    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  


Floating-Point Support
asin, asinf, asinl
atan, atanf, atanl, atan2, atan2f, atan2l
cos, cosf, cosl, cosh, coshf, coshl
sin, sinf, sinl, sinh, sinhf, sinhl
tan, tanf, tanl, tanh, tanhf, tanhl