Calculates the arctangent of x (atan) or the arctangent of y/x (atan2).
double atan( double x );
double atan2( double y, double x );
| Routine | Required Header | Compatibility |
| atan | <math.h> | ANSI, Win 95, Win NT |
| atan2 | <math.h> | ANSI, Win 95, Win NT |
For additional compatibility information, see Compatibility in the Introduction.
Libraries
| LIBC.LIB | Single thread static library, retail version |
| LIBCMT.LIB | Multithread static library, retail version |
| MSVCRT.LIB | Import library for MSVCRT.DLL, retail version |
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