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C atan2()

The atan2() function computes the arc tangent of an argument.

C atan2() Prototype

double atan2(double y, double x);

Function atan2() takes two arguments: x-coordinate and y-coordinate, and calculate the angle in radians for the quadrant.

For better understanding of atan2():

[Mathematics] tan-1(y/x) = atan2(y,x) [In C programming] 

Two other functions atan2f() and atan2l() are also present in C to specifically work with float and long double respectively.

The atan2() function is defined in <math.h> header file.

C atan2() range

The arguments of atan2() can be any number, either positive or negative.

Example: C atan2() function

#include <stdio.h>
#include <math.h>
#define PI 3.141592654

int main()
  double x, y, result;
  y = 2.53;
  x = -10.2;
  result = atan2(y, x);
  result = result * 180.0/PI;

  printf("Tangent inverse for(x = %.1lf, y = %.1lf) is %.1lf degrees.", x, y, result);
  return 0;


Tangent inverse for(x = -10.2, y = 2.53) is 166.1 degrees.

Caution while using atan2()

The value of second argument passed should not be 0. If the second argument passed is 0, the program will not run correctly.