四则运算，即加减乘除，是数学最基本的算术运算。如果加减乘除放在同一个算式列中的话，其计算的顺序是「先乘除，后加减」，括号先算。四则运算的起源很早，几乎在数学产生时就有了。

1. 依中序遍历由左而右计算。
2. 先括号，再× ÷，后 + −（先乘除后加减）。
3. 先算内括号，再算外括号。（因此先算小括号，再算中括号，最后算大括号。）

Elementary arithmetic is the simplified portion of arithmetic that includes the operations of addition, subtraction, multiplication, and division. It should not be confused with elementary function arithmetic.

Elementary arithmetic starts with the natural numbers and the written symbols (digits) that represent them. The process for combining a pair of these numbers with the four basic operations traditionally relies on memorized results for small values of numbers, including the contents of a multiplication table to assist with multiplication and division.