COS 333: Chapter 9, Part 1

Willem van Heerden
14 Sept 202136:31

Summary

TLDRThis lecture delves into the concept of sub-programs, exploring their role in programming languages and their abstraction capabilities. It covers fundamental aspects such as sub-program definitions, headers, calls, and parameters, including formal and actual parameters, as well as parameter profiles and protocols. The lecture also touches on various programming languages' handling of sub-programs, including executable definitions, anonymous functions, and default parameters. It discusses the distinction between procedures and functions, and raises design issues like local variable allocation and the possibility of nested sub-program definitions.

Takeaways

  • 📚 The lecture introduces Chapter 9 focusing on sub-programs, explaining their role in programming languages and fundamental concepts.
  • 🔑 Abstraction is central to modern programming, with process abstraction being discussed in Chapter 9 and data abstraction in Chapter 11.
  • 🕵️‍♂️ Sub-programs, also known as functions or methods, have a single entry point and suspend the execution of the calling program until they complete.
  • 📝 The lecture emphasizes the importance of understanding and using correct terminology when discussing sub-programs for test and exam purposes.
  • 📌 Sub-program definitions include the interface, detailing how the sub-program is called, and the actions, specifying what the sub-program does.
  • 🌐 Executable sub-program definitions in languages like Python can vary depending on execution conditions, affecting program language evaluation criteria.
  • 🏷️ The lecture distinguishes between sub-program headers, which include the name and parameters, and sub-program calls, which are requests to execute a sub-program.
  • 🔄 The correspondence between actual and formal parameters can be ensured by positional or keyword parameters, each with its advantages and disadvantages.
  • 🎯 Default parameters and variable numbers of parameters offer flexibility in how sub-programs can be called, with specific language requirements and behaviors.
  • 🛠️ The lecture discusses design issues related to sub-programs, including local variable allocation (static or dynamic) and the possibility of nested sub-program definitions.
  • ⚙️ Different programming languages handle sub-programs and local variables differently, with implications for recursion, storage sharing, access speed, and history sensitivity.

Q & A

  • What is the main focus of chapter 9 in the textbook?

    -Chapter 9 focuses on sub-programs, discussing their role in programming languages, fundamental concepts, design issues, and local referencing environments.

  • What are the two fundamental facilities that support abstraction in modern programming?

    -The two fundamental facilities that support abstraction are process abstraction and data abstraction, with the latter being supported by abstract data types (ADTs) and object-oriented programming (OOP).

  • What is the difference between a sub-program and a calling program during execution?

    -A sub-program is a part of the code that can be called by another part of the program, the calling program. When a sub-program is called, the execution of the calling program is suspended until the sub-program completes its execution and control returns to the caller.

  • What are the two main components defined by a sub-program definition?

    -A sub-program definition defines the interface of the sub-program, which includes its name, parameter types, and return type, and the actions of the sub-program, which is its body or the operations it performs.

  • How do executable sub-program definitions affect the evaluation criteria of a programming language?

    -Executable sub-program definitions allow for different definitions of the same sub-program to exist based on the execution path, which can affect the predictability and evaluation of the program's behavior in a language.

  • What is the difference between a sub-program header and a sub-program call?

    -A sub-program header is the first part of the sub-program definition that includes the name, type, and formal parameters of the sub-program. A sub-program call is an explicit request to execute the sub-program, which includes the actual parameters passed to the sub-program.

  • What are formal parameters and actual parameters in the context of sub-programs?

    -Formal parameters are the variables listed in the header of the sub-program and used within its body. Actual parameters are the values or addresses passed to the sub-program during a call.

  • What is the purpose of a sub-program declaration?

    -A sub-program declaration provides the protocol of the sub-program, which includes the number, order, and types of parameters, as well as the return type, without providing the body of the sub-program.

  • How do positional parameters ensure the correspondence between actual and formal parameters?

    -Positional parameters ensure correspondence by binding the actual parameters to the formal parameters based on their position in the sub-program call.

  • What are the advantages and disadvantages of using keyword parameters?

    -The advantage of keyword parameters is that they allow parameters to be specified in any order, reducing the chance of errors due to incorrect order. A potential disadvantage is that they may require more code to specify the parameter names, which could make the code more verbose.

  • Why must default parameters appear last in the list of parameters in C++?

    -In C++, default parameters must appear last to ensure that if the function is called with fewer arguments than there are parameters, the correct default values are used without ambiguity.

  • What is the difference between default parameters and a variable number of parameters?

    -Default parameters allow for some parameters to be omitted from a call, using predefined values, while a variable number of parameters allows a sub-program to accept any number of arguments, typically managed as an array or list.

  • Why must all parameters be of the same type when using a variable number of parameters in C#?

    -In C#, the use of the 'params' keyword requires that all parameters be of the same type to ensure consistency when they are treated as an array within the method.

  • What is the distinction between procedures and functions in terms of sub-programs?

    -Procedures are sub-programs that perform actions and may produce results by modifying global variables or parameters passed by reference. Functions are sub-programs that return a value and are generally expected to produce no side effects, although in practice they often do.

  • What are some design issues related to sub-programs in high-level programming languages?

    -Design issues include whether local variables are statically or dynamically allocated, whether sub-program definitions can be nested, the parameter parsing methods provided, parameter type checking, the referencing environment of passed sub-programs, allowing functional side effects, the return types allowed from functions, sub-program overloading, support for generic sub-programs, and closure support for nested sub-programs.

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相关标签
Sub-programsProgramming ConceptsControl StructuresAbstractionParameter PassingFunction DesignRecursion SupportStatic VariablesDynamic VariablesLocal Variable Allocation
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