Edexcel A-Level Programming: Constructs, Data Structures and Algorithms | 爱德思 A-Level 编程：程序结构、数据结构与算法

📚 Edexcel A-Level Programming: Constructs, Data Structures and Algorithms | 爱德思 A-Level 编程：程序结构、数据结构与算法

In Edexcel A-Level Computer Science, programming is not just about writing code; it is about designing solutions, choosing appropriate data structures, and analysing efficiency. This revision guide covers the core programming constructs, essential data structures, and algorithm design techniques that appear across Paper 1 and the programming project.

在爱德思 A-Level 计算机科学中，编程不仅仅是写代码，更是设计解决方案、选择合适的数据结构以及分析算法效率。本复习指南涵盖 Paper 1 和编程项目中常见的核心程序结构、关键数据结构与算法设计方法。

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1. Programming Paradigms and Language Types | 编程范式与语言类型

A programming paradigm is a fundamental style of writing programs. At A-Level, you mainly need to understand the procedural paradigm, where a program is broken into procedures or functions, and the object-oriented paradigm, where data and behaviour are grouped into classes and objects.

编程范式是编写程序的基本风格。在 A-Level 阶段，你需要重点理解过程式范式（将程序拆分为过程或函数）和面向对象范式（将数据和行为组织为类与对象）。

High-level languages such as Python, Java and C# are translated into machine code by compilers or interpreters. A compiler translates the whole source code before execution, while an interpreter translates and executes line by line.

Python、Java 和 C# 等高级语言通过编译器或解释器翻译为机器码。编译器在执行前翻译整个源代码，而解释器逐行翻译并执行。

Procedural code often uses top-down design and stepwise refinement. Object-oriented code uses encapsulation, inheritance and polymorphism to make large systems easier to maintain.

过程式代码通常采用自顶向下设计和逐步求精。面向对象代码通过封装、继承和多态使大型系统更易于维护。

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2. Variables, Constants and Data Types | 变量、常量与数据类型

A variable is a named storage location whose value can change during execution. A constant is a named value that cannot be changed after it is initialised. Using constants improves readability and reduces magic numbers.

变量是命名的存储位置，其值在程序执行期间可以改变。常量是初始化后不可更改的命名值。使用常量可提高可读性并减少“魔法数字”。

Common primitive data types include integer, real/float, Boolean, character and string. Some languages also provide date/time and enumeration types. Choosing the correct type affects memory use and the operations available.

常见的基本数据类型包括整型、实型/浮点型、布尔型、字符型和字符串。一些语言还提供日期/时间和枚举类型。选择正确的类型会影响内存使用和可执行的操作。

Type casting changes a value from one type to another, for example converting the string ’42’ to the integer 42. Implicit casting happens automatically when there is no data loss, while explicit casting must be written by the programmer.

类型转换将值从一种类型转换为另一种类型，例如将字符串 ’42’ 转换为整数 42。隐式转换在没有数据丢失时自动发生，而显式转换必须由程序员编写。

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3. Sequence, Selection and Iteration | 顺序、选择与迭代

Every program is built from three control constructs: sequence, selection and iteration. Sequence means statements execute one after another in order. Selection allows different paths with IF, ELSE IF, ELSE or CASE statements.

所有程序都建立在三种控制结构之上：顺序、选择和迭代。顺序意味着语句按先后顺序执行。选择使用 IF、ELSE IF、ELSE 或 CASE 语句允许执行不同路径。

Iteration repeats a block of code. Count-controlled loops such as FOR run a known number of times, while condition-controlled loops such as WHILE and REPEAT UNTIL run based on a Boolean condition.

迭代重复执行一段代码。计数控制循环（如 FOR）运行已知次数，而条件控制循环（如 WHILE 和 REPEAT UNTIL）根据布尔条件运行。

Pseudocode uses structured English to express logic without syntax concerns. The examples below show selection and iteration.

伪代码使用结构化英语表达逻辑，无需关注语法。下面的示例展示选择和迭代。

IF score ≥ 70 THEN
grade ← ‘Distinction’
ELSE IF score ≥ 40 THEN
grade ← ‘Pass’
ELSE
grade ← ‘Fail’
END IF

FOR i ← 1 TO 10 DO
OUTPUT i
END FOR

WHILE temperature < 20 DO
heater ← TRUE
END WHILE

Notice that FOR is count-controlled; WHILE is condition-controlled. Both are essential for Edexcel problem-solving questions.

请注意 FOR 是计数控制，WHILE 是条件控制。两者对爱德思问题求解题都必不可少。

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4. Arrays and Lists | 数组与列表

A one-dimensional array stores elements of the same data type in contiguous memory locations. Each element is accessed by an index, usually starting at 0 or 1 depending on the language or pseudocode convention used by Edexcel.

一维数组将相同数据类型的元素存储在连续的内存空间中。每个元素通过索引访问，索引通常从 0 或 1 开始，具体取决于语言或爱德思伪代码约定。

A two-dimensional array can be thought of as a table with rows and columns. For example, matrix[2][0] refers to row index 2 and column index 0.

二维数组可以看作由行和列组成的表格。例如，matrix[2][0] 表示行索引为 2、列索引为 0 的元素。

Lists are more flexible than arrays because they can grow and shrink dynamically. Common list operations include append, insert, remove, search and sort.

列表比数组更灵活，因为列表可以动态增长和缩小。常见的列表操作包括追加、插入、删除、搜索和排序。

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5. Stacks and Queues | 栈与队列

A stack is a last-in-first-out (LIFO) structure. The main operations are push, which adds an item to the top, and pop, which removes the top item. Stacks support recursion, undo features and expression evaluation.

栈是一种后进先出（LIFO）结构。主要操作是 push（将项添加到栈顶）和 pop（移除栈顶项）。栈支持递归、撤销功能和表达式求值。

A queue is a first-in-first-out (FIFO) structure. Items are enqueued at the rear and dequeued from the front. Queues model waiting lines, print spooling and CPU scheduling.

队列是一种先进

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