# Divisions with Integer

A pretty common error but I still got burn by it, therefore a note is warranted.

In most programming language, like Ruby, divising Integers will result in an Integer, whether the result is just or not.

It is quite obvious with small operation:

5 / 3 # => 1

But the real danger lies in bigger operation, or operation part of another operation.

I recently fall in this trap when trying to Convert Decimal Degrees into Degrees, Minutes, Seconds.

Let’s take the following code where I use a common formula to convert degrees to degrees, minutes, seconds:

DEG = "\xC2\xB0"
MIN_PER_DEG = 60
SEC_PER_MIN = 60
SEC_PER_DEG = MIN_PER_DEG * SEC_PER_MIN

def dms(dd)
d = dd.to_i                                   # => 76
m = ((dd - d) * MIN_PER_DEG).to_i             # => 43
s = (dd - d - m / SEC_PER_MIN) * SEC_PER_DEG  # => 2628?!

format(%(%d#{DEG}%02d'%02d"), d, m, s)        # => "76°43'2628\""
end

dms(76.73) == %(76°43'48")                      # => false

An honnest mistake but a common one. For this code to run properly, we need to do the calculation with floats; converting m to a float is enough here:

def dms(dd)
d = dd.to_i                                        # => 76
m = ((dd - d) * MIN_PER_DEG).to_i                  # => 43
s = (dd - d - m.to_f / SEC_PER_MIN) * SEC_PER_DEG  # => 48.000000000014296

format(%(%d#{DEG}%02d'%02d"), d, m, s)             # => "76°43'48\""
end

dms(76.73) == %(76°43'48")                           # => true