目录第三章分支语句和编程设计.........................................................................................................13.1自上而下的编程方法简介................................................................................................13.3关系运算符和逻辑运算符................................................................................................43.3.1关系运算符.............................................................................................................43.3.2小心==和~=运算符................................................................................................53.3.3逻辑运算符.............................................................................................................6例3.1.................................................................................................................................73.3.4逻辑函数.................................................................................................................7测试3.1.............................................................................................................................73.4选择结构(分支语句).........................................................................................................83.4.1if结构......................................................................................................................83.4.2if结构举例..............................................................................................................9例3.2.................................................................................................................................9例3.3...............................................................................................................................123.4.3关于if结构使用的注意事项...............................................................................13例3.4...............................................................................................................................143.4.4switch结构....................