The development life cycle and design tools · ⁨开发生命周期与设计工具⁩

Building a program

• A program is built in stages — the program development life cycle 程序开发生命周期.
• We plan it with design 设计 tools, then write the algorithm.
• Every algorithm breaks into input → processing → output.

The four stages

• Analysis 分析 — study the problem and work out what's needed.
• Design — plan how the program will work.
• Coding 编码 — write the code, testing 测试 small parts as you go (iterative testing).
• Testing — run the finished program with test data to find errors.
• Two analysis skills: abstraction 抽象 (keep only the important details) and decomposition 分解 (break a big problem into smaller parts).

The four stages of program development; testing feeds back to fix and refine the design.

Design tools

• A structure diagram — shows the parts of a system and how they fit together.
• A flowchart 流程图 — boxes and arrows showing the steps in order.
• Pseudocode 伪代码 — steps in simple, code-like English (not a real language).

Software is written by programmers who follow the development life cycle.

Input, processing, output

• Every algorithm decomposes into input (the data in), processing (the work done), and output (the result).
• e.g. "average of three marks": input the 3 marks → add them and divide by 3 → output the average.

A program flowchart sets out the steps and decisions of a program during the design stage.

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