CMPUT 201: Understanding Unix and C

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Questions and Answers

What is the purpose of the '#include' directive in a C program?

To specify the data types used in the program.

To define the main function of the program.

To include libraries necessary for the program. (correct)

To declare variables used in the program.

What is the correct return value of the main function if the program runs successfully?

-1

None

0 (correct)

Which function is responsible for reading user input from the keyboard in a C program?

printf

scanf (correct)

input

getchar

How does the compilation process in C differ from the execution of a Python program?

Python stops at the first error, while C compiles the whole program. Signup and view all the answers

What will happen if you try to run a C program with a syntax error?

The program will compile, but not execute. Signup and view all the answers

What is a primary strength of the C programming language?

It offers efficiency and low-level access to machine concepts. Signup and view all the answers

Which programming languages have been influenced by C?

C++, Java, C#, Perl Signup and view all the answers

What common characteristic do most versions of UNIX and C share?

C was developed as a byproduct of UNIX. Signup and view all the answers

What does the option '-Wall' do when compiling a C program?

Enables all warnings during compilation. Signup and view all the answers

What is a notable weakness of C?

It is error-prone and can be difficult to modify. Signup and view all the answers

What command is commonly used to display the contents of a file in the UNIX shell?

cat Signup and view all the answers

What is the purpose of the 'main' function in a C program?

It is the entry point for the program execution. Signup and view all the answers

What will happen if no '-o' option is provided in the gcc command?

The output will be stored in a file named a.out. Signup and view all the answers

Which tool is necessary for Windows users to connect to a UNIX-based lab computer?

PuTTY Signup and view all the answers

Why is understanding C beneficial for learning higher-level programming languages?

It allows developers to appreciate underlying machine operations. Signup and view all the answers

Which of the following describes how global variables are treated in a C program?

They can be accessed by any function within the program. Signup and view all the answers

What is indicated by the POSIX threads in the context of UNIX?

A standard for thread programming. Signup and view all the answers

What type of output file is generated when compiling a C program without any errors?

Executable file (.exe) Signup and view all the answers

What does the 'void' keyword indicate in the function declaration?

The function does not return any value. Signup and view all the answers

Which of the following is a requirement for naming variables in C?

Variable names cannot include special characters other than _. Signup and view all the answers

Why is it recommended to use self-explanatory names for identifiers?

It reduces the need for comments. Signup and view all the answers

What type of statement is 'scanf("%d", &classNumber)' in the given example?

An input statement Signup and view all the answers

What distinguishes C identifiers from keywords?

Identifiers start with a letter, while keywords are reserved words. Signup and view all the answers

Study Notes

Why Use Unix

Dominant operating system for servers
Employs open standards such as POSIX threads
Uses open-source versions like FreeBSD, OpenBSD, and Linux
Offers numerous free software development tools, including gcc, emacs, and gdb

Why Use C

Developed as a byproduct of the Unix operating system
Functions as a higher-level language than assembly
Primarily developed during the 1960s and 1970s, with various language standards evolving over time
Influences modern programming languages like C++, Java, C#, and Perl

Strengths and Weaknesses of C

Strengths

Efficiency, portability, power, flexibility, and standard libraries
Low-level access to machine-level concepts
Small and limited features
Permissive, allowing for direct control of memory

Weaknesses

Error-prone, requiring careful attention to detail
Difficult to understand and modify due to low-level control

Relationship to Other Courses

This course (CMPUT 201) focuses on using the Unix operating system and the C programming language, building a foundation for further software engineering studies.

Relationship to Other Software Engineering Courses

CMPUT 201: Focuses on small-scale programming.
CMPUT 301: Introduces teamwork, object-oriented design.
CMPUT 401: Emphasizes large-scale programming techniques.
CMPUT 402: Covers software quality assurance principles.

Relationship to the "Outside World"

Learning C allows for a deep understanding and appreciation of higher-level programming languages, as it provides insights into the underlying mechanisms and processes.

The Unix/Linux Shell

The lab computers in CMPUT 201 are named ugXX.cs.ualberta.ca, where XX ranges from 00 to 34.
Users with Unix-based operating systems (e.g., Ubuntu or MacOS) can connect to the lab machines using the ssh command in their terminal.
Windows users require an ssh client like PuTTY to establish a connection.

Shell Commands

Commonly used commands include ls, mkdir, cd, cat, vi, gcc, cp, rm, mv, and more.
The man command provides comprehensive documentation on specific commands.
It's encouraged to familiarize oneself with these commands and learn how to search for specific information.

Sample C Program:

Includes the necessary libraries using the #include directive.
Contains the main function, which serves as the entry point of the program.
Employs variables to store data (e.g., classNumber).
Utilizes functions like printf (for printing output to the terminal) and scanf (for reading user input).
Demonstrates the importance of returning a status code of 0 from the main function for successful program execution.

Compiling a C Program:

C is a compiled language, whereas Python is an interpreted language.
Compilers translate the entire program into object code, while interpreters execute one statement at a time.
The gcc compiler is used with options like -Wall (enabling all warnings) and -std=c99 (specifying the C standard) to compile C programs.

Compiling a C Program (Behind the Scenes):

The compilation process involves several stages:
- Preprocessing: Initializes the source code.
- Compiling: Translates the code into assembly code.
- Assembling: Converts assembly code into object code.
- Linking: Combines object code with libraries to create an executable file.

General Form of a C Program

Programs typically begin with directives (e.g., #include for headers or #define for macros).
Global variables are accessible by any function within the file.
The main function is the entry point of the program, responsible for executing the program logic.
Functions consist of a sequence of statements that perform specific tasks.
Variables must be declared with a specific data type (e.g., int, float, char) to indicate the kind of data they will hold.

Documenting and Formatting:

Indentation is used to structure code blocks.
Blank lines enhance readability by separating logical sections.
Single-line comments (//) or multi-line comments (/* */) are used to explain the code's functionality.

Identifiers:

Variable names, function names, macros, and other elements are referred to as identifiers.
Identifiers must start with a letter or an underscore and are case-sensitive.
Certain keywords like int or union are reserved and cannot be used as identifiers.
Choosing meaningful and descriptive names for identifiers improves code readability and understanding.

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Description

This quiz explores the essential features of Unix and the C programming language, including their historical significance and practical applications. Participants will learn about the strengths and weaknesses of C as well as its relationship with Unix. Dive into the world of open-source software development tools and modern programming influences.