Answer 1

According to C++ standard:
The type double provides at least as much precision as float.
The set of values of the type float is a subset of the set of values of the type double.
This means that on some plaforms double type may be the same as float type.

But on most platforms (like PC):

float type is a single precision 32-bit data type that has 7 digits of precision. Its range is from -3.4E38 to 3.4E38.

double type is a double-precision 64-bit data type. It has 15 digits of precision with a range of -1.7E308 to 1.7E308.