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Cx51 User's Guide

Cx51 Introduction Compiling Programs Language Extensions Preprocessor Advanced Programming 8051 Derivatives Error Messages Library Reference Library Files Source Code Standard Types jmp_buf size_t va_list wchar_t Macros CBYTE CWORD DBYTE DWORD FARRAY FCARRAY FCVAR FVAR PBYTE PWORD XBYTE XWORD Routines By Category Buffer Manipulation Routines Character Routines Data Conversion Routines Intrinsic Routines Math Routines Memory Allocation Routines Stream I/O Routines String Routines Variable Length Argument Routines Miscellaneous Routines Include Files SFR Definitions 80c517.h absacc.h assert.h ctype.h float.h intrins.h limits.h math.h rtx51tny.h setjmp.h stdarg.h stddef.h stdio.h stdlib.h string.h Reference _chkfloat_ _crol_ _cror_ _getkey _irol_ _iror_ _lrol_ _lror_ _nop_ _pop_ _push_ _testbit_ _tolower _toupper abs acos acos517 asin asin517 assert atan atan2 atan517 atof atof517 atoi atol cabs calloc ceil cos cos517 cosh exp exp517 fabs floor fmod free getchar gets init_mempool isalnum isalpha iscntrl isdigit isgraph islower isprint ispunct isspace isupper isxdigit labs log log10 log10517 log517 longjmp malloc memccpy memchr memcmp memcpy memmove memset modf offsetof pow printf printf517 putchar puts rand realloc scanf scanf517 setjmp sin sin517 sinh sprintf sprintf517 sqrt sqrt517 srand sscanf sscanf517 strcat strchr strcmp strcpy strcspn strlen strncat strncmp strncpy strpbrk strpos strrchr strrpbrk strrpos strspn strstr strtod strtod517 strtok strtol strtoul switchbank tan tan517 tanh toascii toint tolower toupper ungetchar va_arg va_end va_start vprintf vsprintf Appendix


#include <math.h>

float atan2 (
  float y,    /* denominator for arc tangent */
  float x);   /* numerator for arc tangent */

The atan2 function calculates the arc tangent of the floating-point ratio y / x. This function uses the signs of both x and y to determine the quadrant of the return value. The floating-point value returned by atan2 is a number in the range -π to π.

Return Value

The atan2 function returns the arc tangent of y / x.

For y = 0 and x = 0, atan2NaN.
For y = 0 and x > 0, atan2 → 0.
For y = 0 and x < 0, atan2 → 2π.

See Also

acos, asin, atan

#include <math.h>
#include <stdio.h> /* for printf */

void tst_atan2 (void) {
  float x;
  float y;
  float z;

  x = -1.0;

  for (y = -10.0; y < 10.0; y += 0.1) {
    z = atan2 (y,x);
    printf ("ATAN2(%f/%f) = %f\n", y, x, z);

/* z approaches -pi as y goes from -10 to 0 */
/* z approaches +pi as y goes from +10 to 0 */
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