using_while_and_for_loops.rb

def sum_with_for(min, max)
    total = 0
    # we create the total variable outside of the loop so that we can use it for the sum, we add to it in each iteration  
    return -1 if min > max
    # we can put the return -1 here as we can check the values at this point even before the first loop
    for i in (min..max) do
      total += i
    end
    # for each loop we add total to i (i represents the iteration)
    # example => total = total + 1 on the first loop (total is set at zero), then total = total + 2 on the second loop (total will now be 1 after that first iteration)
    return total
    # we then return total after going through all the iterations
end

def sum_with_while(min, max)
    total = 0
    return -1 if min > max
    # same as above in setting the variables
    while min <= max
      # here we need to use <= to ensure that 100 is added in the final iteration that is true 
      total += min
      # total = total + min, total starts at 0 and then is reset after each iteration, total becomes 1 (0 + 1) after the first iteration and 3 on the second iteration      
      min += 1
      # min is now 2, min = min (1) + 1, so on the next iteration you'll be adding 2     
    end
    return total
    # we return the total when the minimum gets above 100   
end

p sum_with_for(1, 100)

Thanks man!

thanks