📚 Algorithm Writing and Modification | 算法编写与修改
In computer science, an algorithm is a set of step-by-step instructions that solves a problem. In the Cambridge IGCSE Computer Science syllabus, you are expected to write, analyse and modify algorithms using flowcharts and pseudocode.
在计算机科学中，算法是为解决问题而编写的一组逐步指令。在剑桥 IGCSE 计算机科学考纲中，你应能使用流程图和伪代码来编写、分析并修改算法。
1. What is an Algorithm? | 什么是算法？
An algorithm must be precise, unambiguous and finite. It must have a clear start and end, and each step must be simple enough to carry out without confusion.
算法必须精确、无歧义并且有限。它必须有明确的起点和终点，并且每一步都应足够简单，不会引起混乱。
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Input: data given to the algorithm before it begins.
输入：算法开始前提供给它的数据。
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Processing: calculations and decisions performed on the data.
处理：对数据执行的计算和判断。
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Output: the results displayed to the user.
输出：显示给用户的结果。
An algorithm can be written before any programming language is chosen. It describes the logic of a solution, not the exact syntax of a language.
算法可以在选择任何编程语言之前编写。它描述的是解决方案的逻辑，而不是某种语言的具体语法。
2. Flowcharts and Pseudocode | 流程图与伪代码
Flowcharts use standard symbols to show the order of steps in an algorithm. Pseudocode is a text-based way of describing the same logic using simple English-like statements.
流程图使用标准符号来显示算法步骤的顺序。伪代码是一种基于文本的描述方式，用接近英语的简单语句表示相同逻辑。
| Flowchart Symbol | Meaning | 中文含义 |
|---|---|---|
| Oval / rounded rectangle | Start or end | 开始或结束 |
| Parallelogram | Input or output | 输入或输出 |
| Rectangle | Process / calculation | 处理 / 计算 |
| Diamond | Decision with yes/no branches | 判断，包含是/否分支 |
| Arrow | Flow of control | 控制流向 |
In CIE-style pseudocode, assignment is written with the arrow symbol ←. For example, total ← total + 1 means ‘store the value of total + 1 into total’.
在 CIE 风格伪代码
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