First, the meaning of the number:

1, integer: Numbers like -3, -2,-1, 0, 1, 2,3 ... are called integers. The number of integers is infinite. There is no minimum integer and no maximum integer. A natural number is part of an integer.

2. Natural number: a number used to represent the number of objects. For example 1, 2, 3, 4, 5 ... are called natural numbers. The object is not represented by 0. The number of natural numbers is infinite, the smallest natural number is 0, and there is no largest natural number.

3. Decimal: Divide the integer "1" into 10 part, 100 part, 1000 part ... The number of these parts is several tenths, several percent and several thousandths ... which can be expressed in decimal system. ?

(1) Pure decimals and decimals with decimals: decimals whose integer part is O are called pure decimals, and decimals whose integer part is not O are called decimals. ? (2) Finite decimals and infinite decimals: decimals with limited digits are called finite decimals; Decimals with infinite digits are called infinite decimals.

(3) Cyclic decimal: a decimal in which one or several numbers are repeated from a certain place in the decimal part. Such decimals are called cyclic decimals.

(4) Cycle segment: the decimal part of a cycle decimal, and the repeated numbers in turn are called the cycle segment of this decimal. (5) Pure cyclic decimal and mixed cyclic decimal: