📚 Edexcel A-Level Programming: Core Techniques | Edexcel A-Level 编程：核心技术
Edexcel A-Level programming questions test more than just writing code; they require you to trace, analyse, evaluate and design solutions using standard techniques. A strong grasp of data types, control flow, data structures, common algorithms, object-oriented ideas and recursion is essential for both Paper 1 and the programming project.
Edexcel A-Level 编程题目不仅考查编写代码，还要求你追踪、分析、评估并使用标准技术设计解决方案。掌握数据类型、控制流、数据结构、常见算法、面向对象思想和递归对 Paper 1 和编程项目都至关重要。
1. 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 while a program runs. A constant is similar but its value cannot be reassigned after it is set, which improves code reliability and readability.
变量是一个命名的存储位置，其值在程序运行期间可以改变。常量类似，但其值在设置后不能重新赋值，这提高了代码的可靠性和可读性。
Primitive data types include integer, real/float, Boolean and character. Composite types such as strings, arrays and records are built from these primitives and model more complex data.
基本数据类型包括整数、实数/浮点数、布尔值和字符。字符串、数组和记录等复合类型由这些基本类型构建，用于建模更复杂的数据。
Choosing the correct data type affects memory usage, numeric range and precision. Real numbers stored in floating-point form can suffer rounding errors, so equality tests on floats are often unsafe.
选择正确的数据类型会影响内存使用、数值范围和精度。以浮点形式存储的实数可能会产生舍入误差，因此对浮点数进行相等性测试通常不安全。
2. Sequence, Selection and Iteration | 顺序、选择与迭代
The three fundamental control structures are sequence, selection and iteration. Any algorithm can be expressed using combinations of these constructs.
三种基本控制结构是顺序、选择和迭代。任何算法都可以用这些结构的组合来表达。
Selection is implemented with IF...THEN...ELSE statements and switch/case statements. It allows a program to choose between alternative paths based on a Boolean condition.
选择通过 IF...THEN...ELSE 语句和 switch/case 语句实现。它允许程序根据布尔条件在不同路径之间进行选择。
Iteration uses FOR loops for count-controlled repetition and WHILE or REPEAT...UNTIL loops for condition-controlled repetition. Nested loops handle multi-dimensional data and patterns.
迭代使用 FOR 循环进行计数控制重复，使用 WHILE 或 REPEAT...UNTIL 循环进行条件控制重复。嵌套循环用于处理多维数据和模式。
3. Functions and Procedures | 函数与过程
A function returns a single value and is normally called from within an expression. A procedure performs a task but does not return a value, although it can modify arguments passed by reference or change global state.
函数返回单个值，通常在表达式中调用。过程执行任务但不返回值，尽管它可以通过引用传递参数修改实参或改变全局状态。
Parameters may be passed by value or by reference. Pass-by-value creates a copy of the argument, so changes inside the routine do not affect the original. Pass-by-reference gives the routine access to the original data.
参数可以按值传递或按引用传递。按值传递会创建实参的副本，因此例程内部的更改不会影响原始数据。按引用传递使例程能够访问原始数据。
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