static_cast<double>（n）语句

这样你就不想多用显式类型转换了——这正是目的

@万国之父

http://www.stroustrup.com/bs_faq2.html#static-cast
Maybe, because static_cast is so ugly and so relatively hard to type, you*re more likelyto think twice before using one? That would be good, because casts really are mostly avoidablein modern C++.
“让你不想多用显式类型转换”确实是一个理由，虽然只是最后一个理由……

好让你在用强制转换的时候多打点字, 吃些苦头