would the length of a segment or arc be a dicimal number?

I suppose what you mean is, is such a length typically a

**non-integer**. (

*Any* number can be written as a decimal, like 1.0! Any number can also be written as a fraction.)

The answer is that the length of anything at all

**can** be an integer, or not. A length might be something like 12, or 5.2, 1/3 = 0.33333..., or √2 = 1.4142... (that is, integer, terminating decimal, repeating decimal, or irrational). An arc might have any of those lengths, too.

In the real world, if you measure any length, it will be

*more likely* to be non-integer than integer, but there is no reason it

*has* to be. It's just that, in any given size range, there are more non-integers than integers to choose from. And since nothing can be measured exactly, even if I measured it as 12 cm, it might really be 12.001 or something.