Calculates the inverse tangent of a number

#include <math.h>
double atan ( double x  );
float atanf ( float x  );         (C99)
long double atanl ( long double x  );         (C99)

atan( ) implements the inverse tangent function, commonly called arc tangent.

The return value is given in radians, and is thus in the range -p/2 atan(x) p/2.

Example

#ifdef PI
  printf("The symbol PI was already defined.\n");
  long double pi = (long double) PI;
#else
  long double pi = 4.0L * atanl( 1.0L );   // Because tan(pi/4) = 1
#endif
  printf( "Assume pi equals %.17Lf.\n", pi);

This code produces the following output:

Assume pi equals 3.14159265358979324.

See Also

The arc tangent functions for complex numbers: catan( ), catanf( ), and catanl( )