atan, atan2

Calculates the arctangent of x (atan) or the arctangent of y/x (atan2).

doubleatan(double x**);**

doubleatan2(double y**,doublex);**

For additional compatibility information, see Compatibility in the Introduction.

Libraries

Return Value

atan returns the arctangent of *x.*atan2 returns the arctangent of y/x. If x is 0, atan returns 0. If both parameters of atan2 are 0, the function returns 0. You can modify error handling by using the _matherr routine. atan returns a value in the range –π/2 to π/2 radians; atan2 returns a value in the range –π to π radians, using the signs of both parameters to determine the quadrant of the return value.

Parameters

x, y

Any numbers

Remarks

The atan function calculates the arctangent of x. atan2 calculates the arctangent of y/x. atan2 is well defined for every point other than the origin, even if x equals 0 and y does not equal 0.

Example

/* ATAN.C: This program calculates
 * the arctangent of 1 and -1.
 */

#include <math.h>
#include <stdio.h>
#include <errno.h>

void main( void )
{
   double x1, x2, y;

   printf( "Enter a real number: " );
   scanf( "%lf", &x1 );
   y = atan( x1 );
   printf( "Arctangent of %f: %f\n", x1, y );
   printf( "Enter a second real number: " );
   scanf( "%lf", &x2 );
   y = atan2( x1, x2 );
   printf( "Arctangent of %f / %f: %f\n", x1, x2, y );
}

Output

Enter a real number: -862.42
Arctangent of -862.420000: -1.569637
Enter a second real number: 78.5149
Arctangent of -862.420000 / 78.514900: -1.480006

Floating-Point Support Routines

See Also   acos, asin, cos, _matherr, sin, tan