Question

I can’t figure out why a calculation is wrong. I’m trying to calculate the percent of time that the user scores over the median score in my Rails app.

controller

my_scores_over_median_count = 6
total_scores_over_median = 8
@my_over_median_percent = (my_scores_over_median_count / total_scores_over_median) * 100

When I add this to my controller:

puts my_scores_over_median_count
puts total_scores_over_median 
puts @my_over_median_percent

I get:

6 (correct)
8 (correct)
0 (incorrect)

Can someone please help me understand why I’m getting 0 instead of 75 ? Thank you.

Answer 1

classic integer division problem. Change it to this and see it work:

my_scores_over_median_count = 6.0
total_scores_over_median = 8.0
@my_over_median_percent = (my_scores_over_median_count / total_scores_over_median) * 100

Ruby interprets 6 as a ‘Fixnum’ class, essentially an integer. We know this by:

1.9.3-p194 :001 > 6.class
 => Fixnum 

Dividing any number by a Fixnum causes Ruby to do integer math which means any remainder gets thrown out. So:

1.9.3-p194 :004 > 4 / 5
 => 0 
1.9.3-p194 :005 > 4 / 3
 => 1 

If you have a variable that is a Fixnum, and you want to convert it to a float to force floating point division, you use the .to_f method:

1.9.3-p194 :007 > x = 4
 => 4 
1.9.3-p194 :008 > y = 5
 => 5 
1.9.3-p194 :009 > x / y
 => 0 
1.9.3-p194 :010 > x.to_f / y
 => 0.8