1e-9 or -1e9, which one is correct?

Question

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;

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?

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

I am not sure what 1e-9 is meant for?

Answer 1

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

• 1e-9 is 0.000000001; the minus sign applies to the exponent.
• -1e9 is -1000000000.0; the minus sign applies to the number itself.

The e (or E) is the so called exponential notation and it means "times 10-to-the-power-of", 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.