1, according to the different calculation methods, the formula is generally divided into horizontal and vertical;

2. Addition and subtraction can be divided into addition, subtraction and mixed addition and subtraction;

3. According to whether it contains zero, it can be divided into zero-containing formula and zero-free formula.

Expressions refer to expressions listed when calculating numbers (or algebraic expressions), including numbers (or letters instead of numbers) and operation symbols (four operations, powers, roots, factorials, permutations and combinations, etc. ).

The format of the formula is as follows. The same numbers are aligned at both ends, starting with single digits. If you don't carry, you can put ten digits first, but it is not recommended for carrying addition later.

The strict format is carried out according to the following provisions: the horizontal line form of the formula is written gradually from the left side of the horizontal line grid of the math book. ? Vertical calculation: the first addend in horizontal form is written below the second addend, and the negative sign in horizontal form is aligned with the negative sign. The same number of addend, addend and sum must be aligned.