To have another language is to possess a second soul. ~Charlemagne
There are a fairly large number of niggling exceptions to basic pronunciation ruels, based on the position of the sound. Some of the more notable ones include:
as u-, so 五百 wubai is pronounced "ubai"
as i-, so 一个 yige is pronounced "ige"
as ü-, so 豫园 Yuyuan is pronounced "ü-üan"