[3.1神奇的变量](3.1%E7%A5%9E%E5%A5%87%E7%9A%84%E5%8F%98%E9%87%8F.md) [3.2数字的奥秘](3.2%E6%95%B0%E5%AD%97%E7%9A%84%E5%A5%A5%E7%A7%98.md) [3.3字符串是什么东西](3.3%E5%AD%97%E7%AC%A6%E4%B8%B2%E6%98%AF%E4%BB%80%E4%B9%88%E4%B8%9C%E8%A5%BF.md) [3.4变量的可变性](3.4%E5%8F%98%E9%87%8F%E7%9A%84%E5%8F%AF%E5%8F%98%E6%80%A7.md) [3.5变量取名字很讲究](3.5%E5%8F%98%E9%87%8F%E5%8F%96%E5%90%8D%E5%AD%97%E5%BE%88%E8%AE%B2%E7%A9%B6.md) [3.6变量学习小结](3.6%E5%8F%98%E9%87%8F%E5%AD%A6%E4%B9%A0%E5%B0%8F%E7%BB%93.md) [3.7趣味小挑战](3.7%E8%B6%A3%E5%91%B3%E5%B0%8F%E6%8C%91%E6%88%98.md)