#!/usr/bin/env ruby # -*- coding: utf-8 -*- def kake(kakerareru, kakeru) if kakerareru < 0 || kakeru < 0 return nil end return kakerareru*kakeru end puts "掛け算をします。" print "かけられる数を入力:" suzi1 = gets.to_f print "かける数を入力:" suzi2 = gets.to_f printf("解答%.3fです。\n",kake(suzi1,suzi2))