C/math.h/atan2

    
//Header file: #include <math.h>  
//Declaration: float atan2f(float a, float b); 
               double atan2(double a, double b); 
               long double atan2l(long double a, long double b);  
    
  

  #include <math.h>
  #include <stdio.h>
  int main(void)
  {
    double val = -1.0;
    do {
      printf("Atan2 of %f is %f.\n", val, atan2(val,1.0));
      val += 0.1;
    } while(val<=1.0);
    return 0;
  }
         
/*
Atan2 of -1.000000 is -0.785398.
Atan2 of -0.900000 is -0.732815.
Atan2 of -0.800000 is -0.674741.
Atan2 of -0.700000 is -0.610726.
Atan2 of -0.600000 is -0.540420.
Atan2 of -0.500000 is -0.463648.
Atan2 of -0.400000 is -0.380506.
Atan2 of -0.300000 is -0.291457.
Atan2 of -0.200000 is -0.197396.
Atan2 of -0.100000 is -0.099669.
Atan2 of 0.000000 is 0.000000.
Atan2 of 0.100000 is 0.099669.
Atan2 of 0.200000 is 0.197396.
Atan2 of 0.300000 is 0.291457.
Atan2 of 0.400000 is 0.380506.
Atan2 of 0.500000 is 0.463648.
Atan2 of 0.600000 is 0.540420.
Atan2 of 0.700000 is 0.610726.
Atan2 of 0.800000 is 0.674741.
Atan2 of 0.900000 is 0.732815.
Atan2 of 1.000000 is 0.785398.
*/