1e-9 或 -1e9，哪一个是正确的？ [关闭]

我被分配了一些旧代码，当我阅读它时，我注意到它的形式如下：

float low = 1e-9;
float high = 1e9;

float lowB = 1e-9;
float highB = 1e9;

float lowL = 1e-9;
float highL = 1e9;

所以我看到它试图使用 e 表示法定义一些范围，对吧？但不是1e-9应该是-1e9?

那么这些值将介于-1000000000 and 1000000000, right?

我不知道什么1e-9是为了？

两者都不比另一个更正确。它们只是代表不同的价值观。

1e-9 is 0.000000001;减号适用于指数。

-1e9 is -1000000000.0;减号适用于数字本身。

The e (or E) means "times 10-to-the", so 1e9 is "one times ten to the ninth power", and 1e-9 means "one times ten to the negative ninth power". In mathematical scientific notation, this is usually denoted by a superscript: 1 × 10^-9 or -1 × 10⁹. Programming languages adopted the e or E notation because it was easier to type and print than a superscript (and still is, for that matter). (I think this may have been introduced by Fortran in the 1950s, but I'm not sure of the exact history.)