In some cases such expression
...some loop
solution = n[0].to_s+a[0]+n[1].to_s+a[1]+n[2].to_s+a[2]+n[3].to_s+a[3]+n[4].to_s+a[4]+n[5].to_s
puts solution if eval(solution) == 100
#=> `eval': divided by 0 (ZeroDivisionError)
how to prevent this situation or, maybe, skip loop calculation and continue
if you really just want to skip the current calculation and step forward, the simplest way would be a begin-rescue statement
loop do
begin
solution = n[0].to_s+a[0]+n[1].to_s+a[1]+n[2].to_s+a[2]+n[3].to_s+a[3]+n[4].to_s+a[4]+n[5].to_s
puts solution if eval(solution) == 100
rescue ZeroDivisionError
# catch error
end
end