练习4：变量和命名–笨方法学ruby在线

你已经学会了打印出东西和数学运算。下一步你要学的是「变量」。在开发程序中，变量只不过是用来代表某个东西的名称。开发人员通过使用变量名称可以 让他们的程序读起来更像英语。而且因为开发人员的记性都不怎样，变量名称可以让他们更容易记住程序的内容。如果他们没有在写程序时使用好的变量名称，在 下一次读到原来写的程序码时对他们会大为头疼的。

如果你被这章练习难住了的话，记得我们之前教过的：找到不同点、注意细节:

1. 在每一行的上面写一行注释，给自己解释一下这一行的作用。
2. 倒着读你的.rb文档。
3. 朗读你的.rb文档，将每个字符也朗读出来。

<span class="nv">cars</span> <span class="o">=</span> 100 <span class="nv">space_in_a_car</span> <span class="o">=</span> 4.0 <span class="nv">drivers</span> <span class="o">=</span> 30 <span class="nv">passengers</span> <span class="o">=</span> 90 <span class="nv">cars_not_driven</span> <span class="o">=</span> cars - drivers <span class="nv">cars_driven</span> <span class="o">=</span> drivers <span class="nv">carpool_capacity</span> <span class="o">=</span> cars_driven * space_in_a_car <span class="nv">average_passengers_per_car</span> <span class="o">=</span> passengers / cars_driven puts <span class="s2">"There are #{cars} cars available."</span> puts <span class="s2">"There are only #{drivers} drivers available."</span> puts <span class="s2">"There will be #{cars_not_driven} empty cars today."</span> puts <span class="s2">"We can transport #{carpool_capacity} people today."</span> puts <span class="s2">"We have #{passengers} passengers to carpool today."</span> puts <span class="s2">"We need to put about #{average_passengers_per_car} in each car."</span>

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<span class="nv">cars</span> <span class="o">=</span> 100 <span class="nv">space_in_a_car</span> <span class="o">=</span> 4.0 <span class="nv">drivers</span> <span class="o">=</span> 30 <span class="nv">passengers</span> <span class="o">=</span> 90 <span class="nv">cars_not_driven</span> <span class="o">=</span> cars - drivers <span class="nv">cars_driven</span> <span class="o">=</span> drivers <span class="nv">carpool_capacity</span> <span class="o">=</span> cars_driven * space_in_a_car <span class="nv">average_passengers_per_car</span> <span class="o">=</span> passengers / cars_driven   puts <span class="s2">"There are #{cars} cars available."</span> puts <span class="s2">"There are only #{drivers} drivers available."</span> puts <span class="s2">"There will be #{cars_not_driven} empty cars today."</span> puts <span class="s2">"We can transport #{carpool_capacity} people today."</span> puts <span class="s2">"We have #{passengers} passengers to carpool today."</span> puts <span class="s2">"We need to put about #{average_passengers_per_car} in each car."</span>

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