cmpt 214 part1: L00,L01,L02,L03,A1,Lab 1,L010

Question 1

What is used to control access to a UNIX system?

Answer 1

A combination of a User ID and a password.

Question 2

How is the UNIX filesystem structured?

Answer 2

It uses a hierarchical structure with directories and subdirectories.

Question 3

What is meant by the UNIX filesystem being a single-root directory structure?

Answer 3

All files and directories stem from a single root directory, denoted by /. Every file or directory in UNIX can be traced back to the root.

Question 4

How do you represent the absolute path of a file?

Answer 4

Absolute paths start from the root /, e.g., /home/user/file.txt.

Question 5

What is the working directory in UNIX?

Answer 5

The working directory is the current directory where you are operating. You can find it using the pwd (print working directory) command.

Question 6

What is an absolute path?

Answer 6

An absolute path starts from the root / and specifies the location of a file or directory fully, e.g., /home/user/documents.

Question 7

What is the difference between external programs and built-in commands in UNIX?

Answer 7

Built-in commands are part of the shell itself (e.g., cd, echo), while external programs are separate executables stored in the filesystem (e.g., grep, ls, cat).

Question 8

How can you check if a command is built-in?

Answer 8

Use the type command, e.g., type cd will tell you if cd is a shell built-in.

Question 9

Command: let vs. $((…)) for Arithmetic
Q: How do you use let for arithmetic in UNIX?
Q: How do you use $((…)) for arithmetic in UNIX?

Answer 9

A: let is used for arithmetic evaluation. Example: let result=5+3 assigns 8 to the variable result.
A: $((…)) also performs arithmetic. Example: result=$((5 + 3)) assigns 8 to the variable result.

Question 10

Redirection
Q: What is input redirection?
Q: What is output redirection?
Q: How do you append output to a file?

Answer 10

A: Input redirection takes input from a file instead of the keyboard. Example: command < input.txt.
A: Output redirection sends the output of a command to a file instead of the screen. Example: command > output.txt.
A: Use&raquo_space; to append output. Example: echo “Text”&raquo_space; file.txt.

Question 11

Mounting Filesystems
Q: What does mounting a filesystem mean in UNIX?

Answer 11

A: Mounting means making a filesystem accessible under a directory. For example, mount /dev/sda1 /mnt mounts the /dev/sda1 partition at /mnt.

Question 12

Pipelines
Q: What is a pipeline in UNIX?

Answer 12

A: A pipeline uses the | symbol to pass the output of one command as input to another. Example: cat file.txt | grep “keyword”.

Question 13

Pipeline Example: tr
Q: How does the tr command work in a pipeline?

Answer 13

A: tr translates or deletes characters. Example: cat file.txt | tr ‘a-z’ ‘A-Z’ converts all lowercase letters to uppercase.

Question 14

Recap of Key Spacing Rules:
Spaces required:
Between commands and their arguments.
Inside conditionals and loops.
Around comparison operators and arithmetic with expr.

Answer 14

**Spaces not allowed:
In variable assignments (x=5).
Inside arithmetic expansion ($((5+3))).
Between function names and parentheses (my_function()).

Question 15

cat vs. echo
Q: What’s the difference between cat and echo?

Answer 15

A: cat is used to display file contents, whereas echo outputs text or the value of a variable to the terminal.

Question 16

Command: cat
Q: What does the cat command do in UNIX?

Answer 16

: The cat command concatenates and displays the content of files.

Question 17

Q: How would you use cat to display the content of a file named “file.txt”?

Answer 17

cat file.txt

Question 18

Filesystem Layers
Q: Name the layers of the UNIX system.

Answer 18

A: Hardware, Drivers, Kernel, Utilities, and User Applications.

Question 19

Q: What tools can be used to monitor processes in UNIX?

Answer 19

A: top and htop.

Question 20

Command Structure
Q: What is the general format for UNIX commands?

Answer 20

A: command -[options] [arg1] [arg2] … [argn] RETURN.

(return-> keystroke for excution into the terminal)

Question 21

Help and Manual Pages
Q: How can you display a help message for a UNIX command?
Help and Manual Pages
Q: How can you display a help message for a UNIX command?

Answer 21

: By using command –help.
:by using the man command (e.g., man ls)

Question 22

Bash Scripting
Q: How do you make a Bash script executable?

Answer 22

A: By using the command chmod +x scriptname.sh.

Question 23

Q: What is the purpose of #!/bin/bash in a Bash script?

Answer 23

A: It specifies that the script should run in the Bash shell.

Question 24

Q: How do you assign and access variables in Bash?

Answer 24

A: Use = for assignment and $ for access (e.g., x=5, echo $x).

Question 25

write an if-else statement in Bash

Answer 25

if [ condition ]
then
commands
else
commands
fi

Question 26

while loop written in Bash

Answer 26

while [ condition ]
do
commands
done

Question 27

Special Directories: . and ..
Questions:
What does the . directory represent in UNIX?
What does the .. directory represent in UNIX?
How do you move up two levels in the directory structure?
How would you list files in the current directory using .?
Can you execute a file in the current directory using .?

Answer 27

The . (dot) directory refers to the current directory you’re in. It is a shorthand way to refer to the working directory. For example, ./script.sh runs the script.sh file in the current directory.

The .. (double dot) directory refers to the parent directory of the current directory. For example, if you are in /home/user, using cd .. would move you to /home.

Use cd ../.. to move up two levels in the directory structure. Each .. moves up one level.

You can use ls . to list the files in the current directory, although simply typing ls without . also works.

Yes, to execute a script or program in the current directory, you prefix it with ./, like ./myscript.sh.

Question 28

What are stdin, stdout, and stderr in UNIX?

Answer 28

These are special files that handle input (0), output (1), and error messages (2).

Question 29

What is a computer program?

Answer 29

A computer program is a collection of instructions designed to solve a specific problem. These instructions form the steps of an algorithm.

Question 30

Why are computers referred to as “dumb”?

Answer 30

Computers only perform operations they are instructed to do, not what we want. They execute simple instructions like addition or comparison.

Question 31

What is an assembly language?

Answer 31

Assembly language is a low-level programming language where each statement corresponds to a specific machine instruction. It is not portable across different types of processors.

Question 32

Why are high-level languages more portable than assembly languages?

Answer 32

High-level languages are machine-agnostic, meaning they can run on different systems because they don’t rely on the specific architecture of a processor. This is in contrast to assembly language, which is machine-dependent.

Question 33

What’s an OS?

Answer 33

An operating system (OS) manages the computer’s hardware and software resources and handles the execution of processes. Examples include Unix, Linux, and Windows.

Question 34

How does Unix differ in terms of portability?

Answer 34

Unix, being written in C and making few assumptions about the system’s architecture, has been ported to many different types of computers with minimal effort.

Question 35

What are the steps in compiling a program?

Answer 35

Preprocessing
Compiling
Assembling
Linking These steps convert source code into machine code that can be executed.

Question 36

What is the difference between compiling and linking?

Answer 36

Compiling: Converts the source code into assembly language or object code.

Linking: Combines the object code with libraries to produce the final executable

Question 37

Why do we need to use ./ before executing a program in Unix?

Answer 37

In Unix, ./ is required to explicitly tell the system to run the program in the current directory (since the current directory is not part of the PATH environment by default).

Question 38

purpose of the Makefile?

Answer 38

A Makefile automates the build process by specifying how to compile and link programs. It contains targets, dependencies, and recipes (commands) for building the software.

Question 39

What is a “target” in a Makefile?

Answer 39

A target in a Makefile is the file that is to be created (e.g., an executable or an object file). It is built using a set of instructions specified in the Makefile.

Question 40

What does the clean target do in a Makefile?

Answer 40

The clean target removes all files produced by the build process, usually with the rm command.

Question 41

the role of the .PHONY target in Makefiles?

Answer 41

The .PHONY target tells make that the targets like all and clean are not real files, preventing confusion if files with those names exist.

Question 42

: Explain the #include <stdio.h> line in C.</stdio.h>

Answer 42

This line includes the Standard Input Output (stdio) library, which allows the program to use functions like printf().

Question 43

What is the purpose of int main(void) in a C program?

Answer 43

It defines the main function of the program, where execution begins. It returns an integer value and takes no arguments (void).

Question 44

What does the printf() function do?

Answer 44

The printf() function outputs formatted text to the console. For example, printf(“x is %d”, x); prints the value of the variable x.

Question 45

compiling a C program using gcc?

Answer 45

the command gcc myprog.c -o myprog where myprog.c is the source file and myprog is the resulting executable.

Question 46

How is the %d specifier used in printf()?

Answer 46

%d is a format specifier used in printf() to print an integer value.

Question 47

Topic - Makefile Syntaxes

Explanation: A Makefile contains rules in the form of:

Answer 47

Target: The file you want to create.
Dependencies: Files that must exist before the target is built.
Recipe: Commands to execute, indented by a tab

Example:
target: dependencies
recipe

Question 48

Makefile Variables Allocation

Explanation: Variables in Makefiles store values that can be reused. They are assigned with = and referenced using $(VARIABLE_NAME).

Answer 48

CC = gcc
CFLAGS = -Wall
myprog: myprog.o
$(CC) $(CFLAGS) -o myprog myprog.o

(Here, CC is assigned the compiler gcc, and CFLAGS stores the flags passed to the compiler.)

Question 49

C Basics

Answer 49

Every program starts with the main() function.
Variables must be declared with a type (e.g., int, float).
Functions like printf() and scanf() handle input and output.
Statements are terminated with semicolons (;).
Memory is managed manually, and arrays, pointers, and structures are key data structures.

Question 50

7 Best Friends of Programmers

Answer 50

man: Displays manual pages for command-line tools.
make: Automates building processes with Makefiles.
find/grep: Search tools for finding files or patterns in files.
git/vcs: Version control systems for managing code history (e.g., Git).
gdb: A debugger for analyzing and controlling program execution.
awk/sed: Text-processing utilities for stream editing and data extraction.

Question 51

find: Searches for files in directories based on criteria like name or modification time.
grep: Searches within files for patterns using regular expressions.

Answer 51

find . -name “*.c”
grep “main” myprog.c

Question 52

git/vcs (Version Control Systems)

Answer 52

git init
git add .
git commit -m “Initial commit”
git push

Question 53

awk: Used for pattern scanning and processing. It reads input line by line, applies patterns, and performs actions.
sed: A stream editor that can search, find, and replace text

Answer 53

awk ‘{print $1}’ file.txt
sed ‘s/foo/bar/’ file.txt

Question 54

GDB and Its Commands

Answer 54

gcc -g myprog.c -o myprog
gdb ./myprog
(gdb) run
(gdb) break main # Break at the start of main()
(gdb) break 25 # Break at line 25
(gdb) next # to step over
(gdb) step #step into
(gdb) continue # to Resume execution after hitting a breakpoint.
(gdb) backtrace # to View the call stack to see the sequence of function calls.

Question 55

Data Types in C

Answer 55

int: Represents integers.
float: Represents floating-point numbers.
double: A floating-point type with double the precision of float.
char: Represents a single character.
_Bool: Represents boolean values (true or false) as of the C99 standard

Question 56

Constants

Answer 56

Constants are fixed values that do not change during the program execution. Examples include:

Integer: 58
Character string: “Programming in C is fun.\n”
Constant expressions consist entirely of constant values, e.g., 128 + 7 - 17.

Question 57

Integer Constants

Answer 57

12000 (valid)
12 000 (invalid)

The printf() function formats integers using %i or %d, and can display octal and hexadecimal with %o and %x respectively.

Question 58

Variable Storage and Ranges

Answer 58

Each data type has a defined range determined by its allocated storage. For example, int must be at least 16 bits but can vary based on the system (commonly 32 or 64 bits).

Question 59

Floating-Point Constants

Answer 59

A floating-point constant includes a decimal point. Examples include 3.0, 125.8, and -.0001. Use %f in printf() to display floating-point numbers.

Question 60

Floating-Point Scientific Notation

Answer 60

Floating-point constants can be expressed in scientific notation (e.g., 1.7e4). The mantissa precedes e, and the exponent follows. Use %e in printf().

Question 61

Extended Precision with double

Answer 61

The double type allows for approximately twice the precision of float, using 64 bits of storage. All floating-point constants are treated as double unless specified as float (e.g., 12.5f).

Question 62

:Considerations for Floats and Doubles- Precision and Representation

Answer 62

Floats and doubles are stored according to the IEEE 754 standard. Precision can affect calculations, as small differences may arise due to representation issues.

Question 63

Division (/)

Answer 63

int a = 20, b = 4;
int result = a / b; // result = 5
printf(“%d\n”, result);

Question 64

Character Constants - The char Type

Answer 64

A char variable stores a single character, represented in single quotes (e.g., ‘a’). It can also represent special characters like the newline character (‘\n’).

Question 65

Boolean Type in C

Answer 65

The _Bool type can only store values 0 (false) or 1 (true). It’s used for logical conditions, such as file reading status.

Insight:

Question 66

Type Specifiers in C

Answer 66

Type specifiers modify the storage size and range of variables:

long: Extended range (e.g., long int factorial;)
short: Smaller storage (e.g., short int age;)
unsigned: Only positive values (e.g., unsigned int counter;)

Question 67

Operator Precedence in C

Answer 67

Operators of the same precedence are evaluated based on their associativity (left-to-right or right-to-left).

Question 68

How does the size of an int in C influence the range of values it can store, and what implications does this have for variable selection?

Answer 68

The size of int can vary (commonly 32 or 64 bits).
Determines the range: at least ±32,768 for a 16-bit int and ±2,147,483,647 for a 32-bit int.

Implications:
Memory Efficiency: Use short for small numbers to save space.
Data Integrity: Choosing a type that fits data prevents overflow.

Question 69

Explain the difference between float and double, and provide an example of when you might prefer one over the other.

Answer 69

Difference:
float: 32 bits, ~7 decimal digits of precision.
double: 64 bits, ~15 decimal digits of precision.

Example:
Use float for graphics applications where performance is critical, and precision is less crucial.
Use double for scientific calculations requiring high precision.

Question 70

Modulus (%)

Answer 70

int a = 29, b = 5;
int result = a % b; // result = 4
printf(“%d\n”, result);

Question 71

What is a pointer in C?

Answer 71

A variable that stores the memory address of another variable.

Question 72

What does the & operator do?

Answer 72

It returns the memory address of a variable.

Question 73

What is the difference between a pointer and an array?

Answer 73

An array is a collection of elements, while a pointer holds the address of a single variable (or the first element of an array).

Question 74

Explain what NULL means in the context of pointers.

Answer 74

NULL is a special value that indicates a pointer does not point to any valid memory location.

Question 75

What is a dangling pointer?

Answer 75

A pointer that references memory that has been deallocated or released, leading to undefined behavior if accessed.

Question 76

What does pointer arithmetic allow you to do?

Answer 76

It allows you to navigate through an array by performing operations like addition or subtraction on pointer values.

Question 77

How do you initialize a pointer?

Answer 77

By assigning it the address of a variable, e.g., int *ptr = &variable;.

Question 78

What is a const pointer, and why is it used?

Answer 78

A const pointer is a pointer whose address cannot change after initialization, helping prevent accidental changes to what it points to.

Question 79

What does a double pointer represent?

Answer 79

A pointer to a pointer, which can be used to manage dynamic arrays or modify pointer values in functions.

Question 80

What is the purpose of the sizeof operator in pointer usage?

Answer 80

To determine the size of the type being pointed to, which helps in pointer arithmetic and memory allocation.

Question 81

Why is it important to free dynamically allocated memory?

Answer 81

to prevent memory leaks by releasing memory that is no longer needed back to the system.

Question 82

What does the const keyword signify when used with pointers?

Answer 82

It indicates that the data being pointed to should not be modified through that pointer.

Question 83

What does char * const charPtr = &c; signify?

Answer 83

charPtr is a constant pointer to a character, meaning its address cannot change, but the value at that address can.

Question 84

How can you declare a pointer that cannot change the value it points to?

Answer 84

Use const char *charPtr = &c; where charPtr cannot modify the value at the address it points to.

Question 85

What does const char * const charPtr = &c; represent?

Answer 85

Both the pointer and the value it points to are constant; neither can be changed.

Question 86

Why does valuesPtr = values; work without using the address operator?

Answer 86

The name of the array (values) acts as a pointer to its first element.

Question 87

What is the purpose of the strcpy1 function, and why is it incorrect for string literals?

Answer 87

It copies a string from src to dst, but it cannot handle string literals because they are stored in read-only memory.

Question 88

How can pointers facilitate in/out parameters in C functions?

Answer 88

Pointers allow functions to modify the original variable values, enabling multiple return values.

Question 89

In the greaterSum function, what does *largerArr = arr1; do?

Answer 89

It sets the pointer to point to the first array if it has a greater sum than the second array.

Question 90

What is a pointer to a pointer?

Answer 90

a variable that holds the address of another pointer, allowing multiple levels of indirection.

Question 91

how to use a function pointer to modify array values?

Answer 91

Pass a function pointer to a function that iterates through the array and applies the function to each element.

Question 92

final command to create a tarball of the submission files?

Answer 92

ex: tar -cvf le1.tar git.log org.sh

Question 93

to check if the git.log file is not empty?

Answer 93

test -s git.log; echo $?

Question 94

What bash construct is used to check if a directory exists in the script?

Answer 94

if [[ ! -d $target_dir ]]; then