Operators and Expressions in Programming | 编程中的运算符与表达式

📚 Operators and Expressions in Programming | 编程中的运算符与表达式

Operators are the symbols that tell a computer to perform specific mathematical, relational or logical operations. In Edexcel A-Level Computer Science, you must be able to read, write and trace expressions that combine operators and operands.

运算符是告诉计算机执行特定数学、关系或逻辑操作的符号。在 Edexcel A-Level 计算机科学中，你必须能够阅读、编写并追踪结合了运算符和操作数的表达式。

1. Why Operators Matter | 为什么运算符重要

Operators form the core of every executable instruction. Without them, a program could store data but never calculate, compare or decide.

运算符构成了每条可执行指令的核心。没有它们，程序只能存储数据，却无法计算、比较或做出决策。

Arithmetic operators build formulas for prices, coordinates and counters. 算术运算符用于为价格、坐标和计数器构建公式。
Comparison operators drive conditional statements such as IF and WHILE. 比较运算符驱动 IF 和 WHILE 等条件语句。
Logical operators combine multiple true/false conditions in selection. 逻辑运算符在选择结构中组合多个真/假条件。

2. Arithmetic Operators | 算术运算符

The usual arithmetic operators are addition, subtraction, multiplication, division, modulus, integer division and exponentiation. In Python they are written +, -, *, /, %, //, **.

常见的算术运算符包括加、减、乘、除、取模、整除和乘方。在 Python 中它们分别写作 +、-、*、/、%、//、**。

+ addition 加；- subtraction 减；* multiplication 乘
/ division 除；% modulus 取模；// integer division 整除；** exponentiation 乘方

17 % 5 = 2 and 17 // 5 = 3 and 2 ** 3 = 8

Remember that % gives the remainder after division, while // discards the fractional part and returns an integer in Python.

请记住，% 给出除法后的余数，而 // 在 Python 中丢弃小数部分并返回整数。

3. Comparison / Relational Operators | 比较（关系）运算符

Comparison operators compare two values and return a Boolean result: True or False. They are essential in selection and iteration.

比较运算符比较两个值并返回布尔结果：True 或 False。它们在选择和迭代中是必不可少的。

== means equal to；!= means not equal to. == 表示等于；!= 表示不等于。
>, <, >=, <= test order relationships. >、<、>=、<= 测试大小关系。

In Edexcel pseudocode, the symbols may be written as = or == depending on the context, so always check the question wording.

在 Edexcel 伪代码中，符号可能根据上下文写作 = 或 ==，因此务必核对题目措辞。

4. Logical Operators | 逻辑运算符

Logical operators act on Boolean values. Python uses and, or and not. Many pseudocode specifications show AND, OR, NOT.

逻辑运算符作用于布尔值。Python 使用 and、or 和 not。许多伪代码规范显示 AND、OR、NOT。

and returns True only if both operands are True. and 仅当两个操作数都为 True 时才返回 True。
or returns True if at least one operand is True. or 只要有一个操作数为 True 就返回 True。
not reverses the Boolean value. not 反转布尔值。

(age >= 18) and (country == ‘UK’)

The expression above is True only when both the age condition and the country condition are True.

上面的表达式仅当年龄条件和国家条件都为 True 时才为 True。

5. Bitwise Operators | 位运算符

Bitwise operators work on binary representations of integers. They are less common in A-Level exams, but you may need to trace bit-level operations such as AND, OR, XOR, NOT, left shift and right shift.

位运算符对整数的二进制表示进行操作。它们在 A-Level 考试中较少出现，但你可能需要追踪位级运算，例如 AND、OR、XOR、NOT、左移和右移。

& bitwise AND；| bitwise OR；^ bitwise XOR；~ bitwise NOT
<< shifts bits left；>> shifts bits right. << 将位向左移；>> 将位向右移。

Example: 5 & 3 = 1 because 0101 and 0011 produce 0001.

示例：5 & 3 = 1，因为 0101 与 0011 得到 0001。

6. Assignment Operators | 赋值运算符

The basic assignment operator is =. Compound assignment operators combine arithmetic with assignment, which shortens code.

基本赋值运算符是 =。复合赋值运算符将算术与赋值结合起来，可以缩短代码。

x += 5 is equivalent to x = x + 5. x += 5 等价于 x = x + 5。
x *= 2 is equivalent to x = x * 2. x *= 2 等价于 x = x * 2。
x //= 3 and x %= 3 behave similarly for integer division and remainder. x //= 3 和 x %= 3 分别类似地执行整除和取余。

7. Membership and Identity Operators | 成员与身份运算符

Membership operators test whether a value exists in a sequence. Identity operators test whether two references point to the same object in memory.

成员运算符测试一个值是否存在于序列中。身份运算符测试两个引用是否指向内存中的同一个对象。

in returns True if the element is present in a list, string or tuple. in 如果元素存在于列表、字符串或元组中，则返回 True。
not in returns True if the element is absent. not in 如果元素不存在，则返回 True。
is checks identity; == checks equality of value. is 检查身份；== 检查值的相等性。

8. Precedence and Associativity | 优先级与结合性

Operator precedence decides the order in which operations are evaluated. In most languages, brackets have the highest priority, then exponent, then multiplication/division, then addition/subtraction, then comparisons, then logical operators.

运算符优先级决定了运算的求值顺序。在大多数语言中，括号优先级最高，然后是乘方、乘除、加减，再然后是比较运算，最后是逻辑运算。

Parentheses override all default priority rules. 括号覆盖所有默认优先级规则。
*, /, //, % are evaluated before + and -. *、/、//、% 在 + 和 – 之前计算。
and is evaluated after comparisons but before or in Python. 在 Python 中，and 在比较之后、or 之前计算。

Example: 3 + 4 * 2 equals 11, not 14.

示例：3 + 4 * 2 等于 11，而不是 14。

9. Common Pitfalls in A-Level Exam | A-Level 考试常见易错点

Students often confuse = and ==, misuse integer division, or ignore short-circuit evaluation in logical expressions.

学生经常混淆 = 和 ==，误用整除，或忽略逻辑表达式中的短路求值。

Using = for comparison in Python causes a syntax error or unintended assignment. 在 Python 中误将 = 用作比较会导致语法错误或意外赋值。
In many languages, / gives a real result while // gives integer division in Python. 在许多语言中，/ 给出实数结果，而 Python 中的 // 给出整除。
Check whether the question uses pseudocode or Python; operator symbols can differ. 检查题目使用伪代码还是 Python；运算符符号可能不同。

10. Quick Revision Table | 快速复习表

Operator	Meaning 含义	Example 示例
+	Addition 加	3 + 2 = 5
%	Modulus 取模	7 % 4 = 3
//	Integer division 整除	7 // 4 = 1
==	Equal to 等于	5 == 5 → True
and	Logical AND 逻辑与	True and False → False
in	Membership 成员	‘a’ in ‘cat’ → True

Use this table as a quick check before the exam, but always practise tracing full expressions with mixed operators.

在考试前可以用此表快速自查，但务必练习追踪包含混合运算符的完整表达式。

Published by TutorHao | Programming Revision Series | aleveler.com

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Operators and Expressions in Programming | 编程中的运算符与表达式