def game
    first_num = rand(100)
    next_num = rand(100)
    symbol = rand(2)
    case symbol
    when 0
        symbol = '+'
    when 1
        symbol = '-'
    end
    sum = "#{first_num}#{symbol}#{next_num}"
    print("    #{sum}是多少？\n")
    if gets.include?(eval(sum).to_s)
        @red_flowers += 1
        print("    正确！奖励你#{1}朵小红花！\n")
    else
        print("    错误！正确答案是#{eval(sum)}！\n")
    end
    print("    你已经有了#{@red_flowers}朵小红花！\n    说“下一题”继续游戏。\n")
end
print("    两位数加减法算数游戏即将开始！\n    说“开始”进行游戏。\n")
if gets.include?("开始")
    @red_flowers = 0
    game
end
while gets.include?("下一题")
    game
end