0x00. C - Hello, World

• By Julien Barbier

Resources

Read or watch:

• Everything you need to know to start with C.pdf (You do not have to learn everything in there yet, but make sure you read it entirely first)
• Dennis Ritchie
• ["C" Programming Language: Brian Kernighan](https://alx-intranet.hbtn.io/rltoken/W4oygfMgAp5Hyc7o6QuSYQ ""C" Programming Language: Brian Kernighan")
• Why C Programming Is Awesome
• Learning to program in C part 1
• Learning to program in C part 2
• Understanding C program Compilation Process
• Betty Coding Style
• Hash-bang under the hood (Look at only after you finish consuming the other resources)
• Linus Torvalds on C vs. C++ (Look at only after you finish consuming the other resources)

man or help:

• gcc
• printf (3)
• puts
• putchar

Learning Objectives

At the end of this project, you are expected to be able to explain to anyone, without the help of Google:

General

• Why C programming is awesome
• Who invented C
• Who are Dennis Ritchie, Brian Kernighan and Linus Torvalds
• What happens when you type gcc main.c
• What is an entry point
• What is main
• How to print text using printf, puts and putchar
• How to get the size of a specific type using the unary operator sizeof
• How to compile using gcc
• What is the default program name when compiling with gcc
• What is the official C coding style and how to check your code with betty-style
• How to find the right header to include in your source code when using a standard library function
• How does the main function influence the return value of the program

Requirements

C

• Allowed editors: vi, vim, emacs
• All your files will be compiled on Ubuntu 20.04 LTS using gcc, using the options -Wall -Werror -Wextra -pedantic -std=gnu89
• All your files should end with a new line
• A README.md file at the root of the repo, containing a description of the repository
• A README.md file, at the root of the folder of this project, containing a description of the project
• There should be no errors and no warnings during compilation
• You are not allowed to use system
• Your code should use the Betty style. It will be checked using betty-style.pl and betty-doc.pl

Shell Scripts

• Allowed editors: vi, vim, emacs
• All your scripts will be tested on Ubuntu 20.04 LTS
• All your scripts should be exactly two lines long ($ wc -l file should print 2)
• All your files should end with a new line
• The first line of all your files should be exactly #!/bin/bash

More Info

Betty linter

To run the Betty linter just with command betty <filename>:

• Go to the Betty repository
• Clone the repo to your local machine
• cd into the Betty directory
• Install the linter with sudo ./install.sh
• emacs or vi a new file called betty, and copy the script below:

#!/bin/bash
# Simply a wrapper script to keep you from having to use betty-style
# and betty-doc separately on every item.
# Originally by Tim Britton (@wintermanc3r), multiargument added by
# Larry Madeo (@hillmonkey)

BIN_PATH="/usr/local/bin"
BETTY_STYLE="betty-style"
BETTY_DOC="betty-doc"

if [ "$#" = "0" ]; then
    echo "No arguments passed."
    exit 1
fi

for argument in "$@" ; do
    echo -e "\n========== $argument =========="
    ${BIN_PATH}/${BETTY_STYLE} "$argument"
    ${BIN_PATH}/${BETTY_DOC} "$argument"
done

• Once saved, exit file and change permissions to apply to all users with chmod a+x betty
• Move the betty file into /bin/ directory or somewhere else in your $PATH with sudo mv betty /bin/

You can now type betty <filename> to run the Betty linter!

Tasks

0. Preprocessor

mandatory

Write a script that runs a C file through the preprocessor and save the result into another file.

• The C file name will be saved in the variable $CFILE
• The output should be saved in the file c

julien@ubuntu:~/c/0x00$ cat main.c
#include <stdio.h>

/**
 * main - Entry point
 *
 * Return: Always 0 (Success)
 */
int main(void)
{
    return (0);
}
julien@ubuntu:~/c/0x00$ export CFILE=main.c
julien@ubuntu:~/c/0x00$ ./0-preprocessor
julien@ubuntu:~/c/0x00$ tail c
# 942 "/usr/include/stdio.h" 3 4

# 2 "main.c" 2

# 3 "main.c"
int main(void)
{
 return (0);
}
julien@ubuntu:~/c/0x00$

Repo:

• GitHub repository: alx-low_level_programming
• Directory: 0x00-hello_world
• File: 0-preprocessor

1. Compiler

mandatory

Write a script that compiles a C file but does not link.

• The C file name will be saved in the variable $CFILE
• The output file should be named the same as the C file, but with the extension .o instead of .c.
  • Example: if the C file is main.c, the output file should be main.o

julien@ubuntu:~/c/0x00$ export CFILE=main.c
julien@ubuntu:~/c/0x00$ cat main.c
#include <stdio.h>

/**
 * main - Entry point
 *
 * Return: Always 0 (Success)
 */
int main(void)
{
    return (0);
}
julien@ubuntu:~/c/0x00$ ./1-compiler
julien@ubuntu:~/c/0x00$ ls
0-preprocessor  1-compiler   c            main.o
Makefile               100-intel      main.c  main.s
julien@ubuntu:~/c/0x00$ cat -v main.o | head
^?ELF^B^A^A^@^@^@^@^@^@^@^@^@^A^@>^@^A^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^P^B^@^@^@^@^@^@^@^@^@^@@^@^@^@^@^@@^@^K^@^H^@UHM-^IM-eM-8^@^@^@^@]M-C^@GCC: (Ubuntu 5.4.0-6ubuntu1~16.04.2) 5.4.0 20160609^@^T^@^@^@^@^@^@^@^AzR^@^Ax^P^A^[^L^G^HM-^P^A^@^@^\^@^@^@^\^@^@^@^@^@^@^@^K^@^@^@^@A^N^PM-^F^BC^M^FF^L^G^H^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^A^@^@^@^D^@M-qM-^?^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^C^@^A^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^C^@^B^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^C^@^C^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^C^@^E^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^C^@^F^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^C^@^D^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^H^@^@^@^R^@^A^@^@^@^@^@^@^@^@^@^K^@^@^@^@^@^@^@^@main.c^@main^@^@^@^@ ^@^@^@^@^@^@^@^B^@^@^@^B^@^@^@^@^@^@^@^@^@^@^@^@.symtab^@.strtab^@.shstrtab^@.text^@.data^@.bss^@.comment^@.note.GNU-stack^@.rela.eh_frame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
^@^@^@^H^@^@^@^H^@^@^@^@^@^@^@^X^@^@^@^@^@^@^@  ^@^@^@^C^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@M-^P^A^@^@^@^@^@^@^M^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^A^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@julien@ubuntu:~/c/0x00$

Repo:

• GitHub repository: alx-low_level_programming
• Directory: 0x00-hello_world
• File: 1-compiler

2. Assembler

mandatory

Write a script that generates the assembly code of a C code and save it in an output file.

• The C file name will be saved in the variable $CFILE
• The output file should be named the same as the C file, but with the extension .s instead of .c.
  • Example: if the C file is main.c, the output file should be main.s

julien@ubuntu:~/c/0x00$ export CFILE=main.c
julien@ubuntu:~/c/0x00$ cat main.c
#include <stdio.h>

/**
 * main - Entry point
 *
 * Return: Always 0 (Success)
 */
int main(void)
{
    return (0);
}
julien@ubuntu:~/c/0x00$ ./2-assembler
julien@ubuntu:~/c/0x00$ ls
0-preprocessor  1-compiler  2-assembler c  main.c  main.s  Makefile
julien@ubuntu:~/c/0x00$ cat main.s
    .file   "main.c"
    .text
    .globl  main
    .type   main, @function
main:
.LFB0:
    .cfi_startproc
    pushq   %rbp
    .cfi_def_cfa_offset 16
    .cfi_offset 6, -16
    movq    %rsp, %rbp
    .cfi_def_cfa_register 6
    movl    $0, %eax
    popq    %rbp
    .cfi_def_cfa 7, 8
    ret
    .cfi_endproc
.LFE0:
    .size   main, .-main
    .ident  "GCC: (Ubuntu 5.4.0-6ubuntu1~16.04.2) 5.4.0 20160609"
    .section    .note.GNU-stack,"",@progbits
julien@ubuntu:~/c/0x00$

Repo:

• GitHub repository: alx-low_level_programming
• Directory: 0x00-hello_world
• File: 2-assembler

3. Name

mandatory

Write a script that compiles a C file and creates an executable named cisfun.

• The C file name will be saved in the variable $CFILE

julien@ubuntu:~/c/0x00$ export CFILE=main.c
julien@ubuntu:~/c/0x00$ cat main.c
#include <stdio.h>

/**
 * main - Entry point
 *
 * Return: Always 0 (Success)
 */
int main(void)
{
    return (0);
}
julien@ubuntu:~/c/0x00$ ./3-name
julien@ubuntu:~/c/0x00$ ls
0-preprocessor  1-compiler   3-name  cisfun  main.o  Makefile
100-intel       2-assembler  c       main.c  main.s
julien@ubuntu:~/c/0x00$

Repo:

• GitHub repository: alx-low_level_programming
• Directory: 0x00-hello_world
• File: 3-name

4. Hello, puts

mandatory

Write a C program that prints exactly "Programming is like building a multilingual puzzle, followed by a new line.

• Use the function puts
• You are not allowed to use printf
• Your program should end with the value 0

julien@ubuntu:~/c/0x00$ gcc -Wall -Werror -Wextra -pedantic -std=gnu89 4-puts.c && ./a.out
"Programming is like building a multilingual puzzle
julien@ubuntu:~/c/0x00$ echo $?
0
julien@ubuntu:~/c/0x00$

Repo:

• GitHub repository: alx-low_level_programming
• Directory: 0x00-hello_world
• File: 4-puts.c

5. Hello, printf

mandatory

Write a C program that prints exactly with proper grammar, but the outcome is a piece of art,, followed by a new line.

• Use the function printf
• You are not allowed to use the function puts
• Your program should return 0
• Your program should compile without warning when using the -Wall gcc option

julien@ubuntu:~/c/0x00$ gcc -Wall -Werror -Wextra -pedantic -std=gnu89 5-printf.c
julien@ubuntu:~/c/0x00$ ./a.out
with proper grammar, but the outcome is a piece of art,
julien@ubuntu:~/c/0x00$ echo $?
0
julien@ubuntu:~/c/0x00$

Repo:

• GitHub repository: alx-low_level_programming
• Directory: 0x00-hello_world
• File: 5-printf.c

6. Size is not grandeur, and territory does not make a nation

mandatory

Write a C program that prints the size of various types on the computer it is compiled and run on.

• You should produce the exact same output as in the example
• Warnings are allowed
• Your program should return 0
• You might have to install the package libc6-dev-i386 on your Linux (Vagrant) to test the -m32 gcc option

julien@ubuntu:~/c/0x00$ gcc 6-size.c -m32 -o size32 2> /tmp/32
julien@ubuntu:~/c/0x00$ gcc 6-size.c -m64 -o size64 2> /tmp/64
julien@ubuntu:~/c/0x00$ ./size32
Size of a char: 1 byte(s)
Size of an int: 4 byte(s)
Size of a long int: 4 byte(s)
Size of a long long int: 8 byte(s)
Size of a float: 4 byte(s)
julien@ubuntu:~/c/0x00$ ./size64
Size of a char: 1 byte(s)
Size of an int: 4 byte(s)
Size of a long int: 8 byte(s)
Size of a long long int: 8 byte(s)
Size of a float: 4 byte(s)
julien@ubuntu:~/c/0x00$ echo $?
0
julien@ubuntu:~/c/0x00$

Repo:

• GitHub repository: alx-low_level_programming
• Directory: 0x00-hello_world
• File: 6-size.c

Done! Help Check your code Get a sandbox

7. Intel

#advanced

Write a script that generates the assembly code (Intel syntax) of a C code and save it in an output file.

• The C file name will be saved in the variable $CFILE.
• The output file should be named the same as the C file, but with the extension .s instead of .c.
  • Example: if the C file is main.c, the output file should be main.s

julien@ubuntu:~/c/0x00$ export CFILE=main.c
julien@ubuntu:~/c/0x00$ cat main.c
#include <stdio.h>

/**
 * main - Entry point
 *
 * Return: Always 0 (Success)
 */
int main(void)
{
    return (0);
}
julien@ubuntu:~/c/0x00$ ./100-intel
julien@ubuntu:~/c/0x00$ cat main.s
    .file   "main.c"
    .intel_syntax noprefix
    .text
    .globl  main
    .type   main, @function
main:
.LFB0:
    .cfi_startproc
    push    rbp
    .cfi_def_cfa_offset 16
    .cfi_offset 6, -16
    mov rbp, rsp
    .cfi_def_cfa_register 6
    mov eax, 0
    pop rbp
    .cfi_def_cfa 7, 8
    ret
    .cfi_endproc
.LFE0:
    .size   main, .-main
    .ident  "GCC: (Ubuntu 5.4.0-6ubuntu1~16.04.2) 5.4.0 20160609"
    .section    .note.GNU-stack,"",@progbits
julien@ubuntu:~/c/0x00$

Repo:

• GitHub repository: alx-low_level_programming
• Directory: 0x00-hello_world
• File: 100-intel

Done! Help Check your code Get a sandbox

8. UNIX is basically a simple operating system, but you have to be a genius to understand the simplicity

#advanced

Write a C program that prints exactly and that piece of art is useful" - Dora Korpar, 2015-10-19, followed by a new line, to the standard error.

• You are not allowed to use any functions listed in the NAME section of the man (3) printf or man (3) puts
• Your program should return 1
• Your program should compile without any warnings when using the -Wall gcc option

julien@ubuntu:~/c/0x00$ gcc -Wall -Werror -Wextra -pedantic -std=gnu89 -o quote 101-quote.c
julien@ubuntu:~/c/0x00$ ./quote
and that piece of art is useful" - Dora Korpar, 2015-10-19
julien@ubuntu:~/c/0x00$ echo $?
1
julien@ubuntu:~/c/0x00$ ./quote 2> q
julien@ubuntu:~/c/0x00$ cat q
and that piece of art is useful" - Dora Korpar, 2015-10-19
julien@ubuntu:~/c/0x00$ grep printf < 101-quote.c
julien@ubuntu:~/c/0x00$ grep put < 101-quote.c
julien@ubuntu:~/c/0x00$

Repo:

• GitHub repository: alx-low_level_programming
• Directory: 0x00-hello_world
• File: 101-quote.c