11.3 Structured Programming 结构化编程简答

Procedure and function

• Procedure：named module that performs a task；called as a statement and does not return a value in the same way as a function。
• Function：named module that returns one value；its return value can be used in an expression or assignment。

Use a module when a task is repeated/reused, has a clear specific purpose, or makes a complex algorithm manageable。

Benefits of subroutines

• Reduce complexity and simplify the main algorithm。
• Can be called repeatedly from several places。
• Designed and tested once, then reused。
• Tested/debugged independently。
• Changes are made once in the module, improving maintenance。

Parameters and arguments

• Parameter：identifier declared in the module header to receive data。
• Argument：actual value/expression supplied when the module is called。
• BYVAL：a copy is passed；changing the parameter does not change the caller's variable。
• BYREF：the original variable is referenced；changes can affect the caller's variable。

Interface terminology

Module interface specifies：

• Module name and whether procedure/function。
• Number, order, names and data types of parameters。
• Passing method, such as BYVAL/BYREF。
• Function return data type/value。

Example short answer：

CheckNum takes two INTEGER parameters and returns a BOOLEAN value.

When to use a function

Use a function when a module calculates/looks up/tests something and the result is required in an expression。A procedure is suitable for a sequence of actions such as displaying a report or updating several items where no single expression result is required。

Efficient modular code

If a function is called repeatedly inside a loop with unchanged arguments, it returns the same value each time。Call it once before the loop, store the result in a local variable, then reuse that variable。

Other good practice：meaningful identifiers、indentation/white space、comments、local variables and clear parameters。

Exam checklist

• Procedure/function 是否按 return value 区分？
• Parameter 与 argument 是否混淆？
• BYVAL/BYREF 的 effect 是否准确？
• Interface 是否包含 parameter types 和 return type？
• Modular benefits 是否写到 reuse、testing、maintenance？
• Efficiency 是否说明 repeated call 为什么多余及如何缓存 result？

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Procedure/function headers、calls、returns 和 parameter pseudocode 留到代码专项。