Ruby function and if statements inside

I'm having an undefined method + error when I typed this function with if/else statement in Ruby. Any ideas? I'm sure it's pretty stupid on my part.

def residentfee( resident )
  if (resident == 0) 
    fee += (46 * 2)
  else 
    fee += (50 + 2)
  end
end 

print "Enter a number: "
number = gets.chomp.to_i
puts residentfee( number )

What am I doing wrong? Thanks in advance.