📚 A-Level OCR Computer Science: Programming Fundamentals Revision Guide | A-Level OCR 计算机科学：编程基础考点精讲
In A-Level OCR Computer Science, programming fundamentals form the backbone of Component 02: Algorithms and Programming. This section covers essential constructs such as variables, data types, control structures, subroutines, parameter passing, scope, recursion, and the use of an IDE. Mastering these concepts is crucial not only for the written examination but also for the practical programming project. This revision guide breaks down each key topic with clear explanations and examples.
在 A-Level OCR 计算机科学课程中，编程基础是 “算法与编程” 部分的核心。本节涵盖变量、数据类型、控制结构、子程序、参数传递、作用域、递归以及集成开发环境的使用等重要内容。掌握这些概念不仅对笔试至关重要，对实践编程项目也同样关键。本考点精讲将逐一解析每个重点主题，并辅以清晰的解释和示例。
1. Variables, Constants and Data Types | 变量、常量与数据类型
Variables are named storage locations whose values can change during program execution. A variable must be declared with a specific data type such as Integer, Float/Real, String, Boolean, or Char. The data type determines the kind of data that can be stored and the operations that can be performed on it.
变量是命名的存储位置，其值在程序执行期间可以改变。变量必须声明为特定的数据类型，如整型、浮点型/实型、字符串、布尔型或字符型。数据类型决定了所能存储的数据种类以及可以对其执行的操作。
Constants are similar to variables but their values remain fixed throughout the program. They are typically declared with a special keyword (e.g., CONST) and are used to avoid magic numbers, making code more readable and maintainable.
常量与变量类似，但其值在整个程序运行过程中保持不变。常量通常使用特殊关键字（如 CONST）声明，用于避免使用”魔数”，从而提高代码的可读性和可维护性。
Many high-level languages are strongly typed, meaning a variable’s type cannot be changed after declaration, and operations must be type-compatible. However, explicit casting (or conversion) functions like INT(), REAL(), STR() can transform values between types in pseudocode.
许多高级语言是强类型的，即变量的类型在声明后不能更改，操作必须类型兼容。然而，在伪代码中可以使用显式转换函数（如 INT()、REAL()、STR()）在不同类型之间转换值。
For example, in pseudocode:
- DECLARE score : INTEGER
- CONST PI ← 3.14159
伪代码示例：
- DECLARE score : INTEGER
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