顺序结构只能顺序执行，不能进行判断和选择，因此需要分支结构。 一个if语句包含一个布尔表达式和一条或多条语句。 语法 ...

When I first learned to program, it was grasping if statements that helped it all click into place for me. Once you can use if statements, you can build all kinds of useful and interesting tools.