Finding the angle between two bearings is often confusing.[1]



Task

Find the angle which is the result of the subtraction b2 - b1, where b1 and b2 are the bearings.


Input bearings are expressed in the range   -180   to   +180   degrees.

The  result  is also expressed in the range   -180   to   +180   degrees.



Compute the angle for the following pairs:

 20 degrees (b1) and 45 degrees (b2)
 -45 and 45
 -85 and 90
 -95 and 90
 -45 and 125
 -45 and 145
 29.4803 and -88.6381
 -78.3251 and -159.036


Optional extra
 
Allow the input bearings to be any (finite) value.



Test cases

 -70099.74233810938 and 29840.67437876723
 -165313.6666297357 and 33693.9894517456
 1174.8380510598456 and -154146.66490124757
 60175.77306795546 and 42213.07192354373


#include <cmath>
#include <iostream>
using namespace std;
 
double getDifference(double b1, double b2) {
	double r = fmod(b2 - b1, 360.0);
	if (r < -180.0)
		r += 360.0;
	if (r >= 180.0)
		r -= 360.0;
	return r;
}
 
int main()
{
	cout << "Input in -180 to +180 range" << endl;
	cout << getDifference(20.0, 45.0) << endl;
	cout << getDifference(-45.0, 45.0) << endl;
	cout << getDifference(-85.0, 90.0) << endl;
	cout << getDifference(-95.0, 90.0) << endl;
	cout << getDifference(-45.0, 125.0) << endl;
	cout << getDifference(-45.0, 145.0) << endl;
	cout << getDifference(-45.0, 125.0) << endl;
	cout << getDifference(-45.0, 145.0) << endl;
	cout << getDifference(29.4803, -88.6381) << endl;
	cout << getDifference(-78.3251, -159.036) << endl;
 
	cout << "Input in wider range" << endl;
	cout << getDifference(-70099.74233810938, 29840.67437876723) << endl;
	cout << getDifference(-165313.6666297357, 33693.9894517456) << endl;
	cout << getDifference(1174.8380510598456, -154146.66490124757) << endl;
	cout << getDifference(60175.77306795546, 42213.07192354373) << endl;
 
	return 0;
}