How to get the value of exponential power?

Assume that after some computation, matlab give me an output:

a(1)=3.712e-12
a(2)=9.123e-13

How can i got the value of 12 and 13? Assume that a(1) and a(2) is in array a=[a(1) a(2)].

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Edit: to avoid confussion, let me rearrange my question: "Can I get the 'index' (how many zeros in the right of the dot) of the first significant digit from data?". Is this is the only way?

n=1
a(1)=3.712e-12
while 1e1^-n>a(1)
    n=n+1;
end

[Stephen23]

"How can i got the value of 12 and 13?"

You didn't: those are the powers of ten, they are not "values".

What you show are numbers written in E-notation, which is the a common way that scientists, engineers, and researchers write small/large numbers:

https://en.wikipedia.org/wiki/Scientific_notation#E-notation

[Muhammad Yasirroni]

Thank you. But, I already understand that. So, let me rearrange my question: "Can I get the 'index' (how many zeros in the right of the dot) of the first significant digit from data?"

p.s. I edit my question

Answer 1

[Stephen23]

Just use log10:

>> floor(log10(a))
ans =
  -12  -13

The correct answer is [-12,-13], not [12,13] (because these are the powers of ten), but of course you can lose information if you want with abs.

[Muhammad Yasirroni]

Great. Thank you.