[4.1 类型转换](4.1%E7%B1%BB%E5%9E%8B%E8%BD%AC%E6%8D%A2.md) [4.2 选择结构](4.2%E9%80%89%E6%8B%A9%E7%BB%93%E6%9E%84.md) [4.3 循环结构](4.3%E5%BE%AA%E7%8E%AF%E7%BB%93%E6%9E%84.md) [4.4 中断及跳转](4.4%E4%B8%AD%E6%96%AD%E5%8F%8A%E8%B7%B3%E8%BD%AC.md) [4.5 include/require](4.5include-require.md) [4.6 异常处理](4.6%E5%BC%82%E5%B8%B8%E5%A4%84%E7%90%86.md)