Složitější kalkulačka - umí násobit s mezivýsledky jako na papíře

Ukázkový program Složitější kalkulačka, který umí násobit s mezivýsledky jako na papíře. Včetně zdrojového kódu v jazyce Ruby.

# returns string with chosen number of "-"
def make_line(length)
  s = ""
  length.times {s << "-"}
  return s
end

# provides safety input of natural number
def enter_natural(msg)
  a = 0
  while (a <= 0)
    puts msg
    a = gets.strip.to_i
    puts "Cislo nesmi byt mensi nebo rovne nule" if (a <= 0)
  end
  return a
end

puts "Vitejte v programu kalkulacka\n\n"

a = enter_natural("Zadejte prvni cislo:")
b = enter_natural("Zadejte druhe cislo:")

# sefety input of operator
opr = ""
operators = ["+", "-", "*"]
while (! operators.include?(opr))
  puts "Zadejte operator[+/-/*]: "
  opr = gets.strip
  puts "Chybne zadany operator." if (! operators.include?(opr))
end

output = []
output << a.to_s
output << opr + b.to_s
# underline result
output << make_line(output.sort_by{|s| s.length}[-1].length)

case opr
when "+"
output << (a + b).to_s
when "-"
output << (a - b).to_s
when "*"
  product = (a * b).to_s
  # partial results
  if (b > 9)
    (b.to_s.length - 1).downto 0 do |i|
      output << (b.to_s[i].chr.to_i * a).to_s
    end
    output << make_line(product.length)
  end
  output << product
end

# formating output
longest = output.sort_by{|s| s.length}[-1].length

output.length.times do |i|
  if (output[i].length < longest)
    difference = longest - output[i].length
    # reduce number of whitespaces from line 4
    if (i > 3) && (i < output.length - 2)
      difference -= (i - 3)
    end
    difference.times { output[i] = " " + output[i] }
  end
end

# displaying output
puts "\n\n"
output.length.times { |i| puts output[i] + "\n"}