1e-9或-1e9，哪一个是正确的？ [英] 1e-9 or -1e9, which one is correct?

问题描述

我分配了一些旧代码，当我阅读它时，我注意到它有以下形式：

I am assigned some old code and when I was reading through it, I noticed it had these in the form of:

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符号定义一些范围，对吗？但不是 1e-9 应该是 -1e9 ？

So I see that it's trying to define some ranges using the e notation, right? But isn't 1e-9 supposed to be -1e9?

那么值将在 -1000000000 和 1000000000 之间，对吗？

Then the values would be between -1000000000 and 1000000000, right?

我不确定 1e-9 是用于？

推荐答案

两者都不比其他更正确。它们只代表不同的值。

Neither is more correct than the other. They just represent different values.

1e-9 是 0.000000001 ;

-1e9 是 -1000000000.0 ;

e （或 E ）表示乘以10到，因此 1e9 是十分之一到九次方， 1e -9 表示负十次幂的1/10。在数学科学记数法中，这通常由上标表示：1×10 ^-9 或-1×10 ⁹ 。编程语言采用 e 或 E 符号，因为它比上标更容易打字和打印对于这个问题）。 （我认为这可能是Fortran在20世纪50年代，但我不知道确切的历史。）

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.)

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