switch case 流程图

switch case流程图如下：

            +-------------+
            |  switch     |
            | expression  |
            +-------------+
                   |
                   | (expression值)
                   |
           +------------------+
           |  case value1:   |
           |   // 代码块   |
           +------------------+
                   |
                   |
                   |
           +------------------+
           |  case value2:   |
           |   // 代码块   |
           +------------------+
                   |
                   |
                   |
           +------------------+
           |  case value3:   |
           |   // 代码块   |
           +------------------+
                   |
                   |
                   |
           +------------------+
           |    default:    |
           |   // 代码块   |
           +------------------+