include "ConsoleWindow"

local fn Haversine( lat1 as double, lon1 as double, lat2 as double, lon2 as double, miles as ^double, kilometers as ^double )
dim as double deg2rad, dLat, dLon, a, c, earth_radius_miles, earth_radius_kilometers

earth_radius_miles = 3959.0 // Radius of the Earth in miles
earth_radius_kilometers = 6372.8 // Radius of the Earth in kilometers
deg2rad = Pi / 180 // Pi is predefined in FutureBasic

dLat = deg2rad * ( lat2  - lat1 )
dLon = deg2rad * ( lon2 - lon1 )
a = sin( dLat / 2 ) * sin( dLat / 2 ) + cos( deg2rad * lat1 ) * cos( deg2rad * lat2 ) * sin( dLon / 2 ) * sin( dLon / 2 )
c = 2 * asin( sqr(a) )

miles.nil# =  earth_radius_miles * c
kilometers.nil# = earth_radius_kilometers * c
end fn

dim as double miles, kilometers
fn Haversine( 36.12, -86.67, 33.94, -118.4, @miles, @kilometers )

print "Distance in miles between BNA and LAX: "; using "####.####"; miles; " miles."
print "Distance in kilometers between BNA LAX: "; using "####.####"; kilometers; " km."