GolamMostafa:
When two 16-bit binary numbers are multiplied, the result is 32-bit binary; why are you saying that it is 16-bit? Is it a typo mistake?
No, that's not how 8 bit microcontroller CPUs work! They only multiply 8 by 8 to give 16 bits. Anything
more ambitious is handled by the compiler / runtime library.
In C operators return the default integer size always unless one of the arguments is larger. On the ATmega
Arduinos the default integer size is 16 bits, so everything is 16 bit unless you force it otherwise. So
16 x 16 gives 16. 32 x 16 gives 32.
Most implementations of C have 32 bits as the default size, but this is a tiny microcontroller with 2k of
RAM total, everything is chosen for compactness and frugality, hence the default int size is 16 bit.