From your link:

A prime number (or prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself.

-7 is neither natural nor greater than 1, so, no, it's not a prime number.

I can see no -7 (i.e. "negative seven") on the list?

https://en.wikipedia.org/wiki/List_of_prime_numbers

Are you sure? Can you point to a resource which presents -7 as a prime number?

In "C++"
While pushing "Attempt" -7 or -6 turns "false" in test, but it is "true" for -7 (it is a prime number) and "false" for -6 (not prime)