Chapter 6
Every number is composed of digits. There are only 10 digits in our number system: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. The term digit refers to one building block of a number; it does not refer to a number itself. For example, 356 is a number composed of three digits: 3, 5, and 6.
Integers can be classified by the number of digits they contain. For example:
2, 7, and −8 are each single-digit numbers (they are each composed of one digit)
43, 63, and −14 are each double-digit numbers (composed of two digits)
500,000 and −468,024 are each six-digit numbers (composed of six digits)
789,526,622 is a nine-digit number (composed of nine digits)
Non-integers are not generally classified by the number of digits they contain, because you can always add any number of zeroes at the end, on the right side of the decimal point:
That said, non-integers can be classified by how many non-zero digits they have to the right of the decimal point. For example, 0.23, 8.014, and 0.0000079 all have two non-zero digits to the right of the decimal point. (Later, there will be a discussion of decimals that do not terminate, that is, they have an infinite number of non-zero digits to the right of the decimal point.)