Rails - how to perform a math function in a view helper -

in view helper method, want able calculate range between 2 numbers. right doing this:

def show_range  max = @shirts.get_max  min = @shirts.get_min  max-min end 

i know max , min working because can print each of values out. however, when try math function in "module shirtshelper", following error:

undefined method `-' nil:nilclass 

why getting error , can fix it?

you error because max variable nil , there no matching method - on nil. check whether min , max not nil max - min if max && min. however, guess might want provide fallback value (e.g. 0) in case, might looking this

def show_range   max = @shirts.get_max   min = @shirts.get_min    if max && min     max - min   else     0 # fallback value   end end 

or more concise:

def show_range   max = @shirts.get_max   min = @shirts.get_min   max && min ? max - min : 0 end