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0x05-pointers_arrays_strings

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0x05. C - Pointers, arrays and strings

Table of Contents

Author Details

Project Description

  • 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 folder of the project is mandatory
  • Your code should use the Betty style. It will be checked using betty-style.pl and betty-doc.pl
  • You are not allowed to use global variables
  • No more than 5 functions per file
  • You are not allowed to use the standard library. Any use of functions like printf, puts, etc… is forbidden
  • You are allowed to use _putchar
  • You don’t have to push _putchar.c, we will use our file. If you do it won’t be taken into account
  • In the following examples, the main.c files are shown as examples. You can use them to test your functions, but you don’t have to push them to your repo (if you do we won’t take them into account). We will use our own main.c files at compilation. Our main.c files might be different from the one shown in the examples
  • The prototypes of all your functions and the prototype of the function _putchar should be included in your header file called main.h
  • Don’t forget to push your header file

Tasks

0

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0. 98 Battery st.

  • Write a function that takes a pointer to an int as parameter and updates the value it points to to 98.

    • Prototype: void reset_to_98(int *n);
julien@ubuntu:~/0x05$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 0-main.c 0-reset_to_98.c -o 0-98
julien@ubuntu:~/0x05$ ./0-98 
n=402
n=98



  • Repo
    • GitHub repository: alx-low_level_programming
    • Directory: 0x05-pointers_arrays_strings
    • File: 0-reset_to_98.c
    • Example file: 0-main.c

1

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1. Don't swap horses in crossing a stream

  • Write a function that swaps the values of two integers.

    • Prototype: void swap_int(int *a, int *b);
julien@ubuntu:~/0x05$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 1-main.c 1-swap.c -o 1-swap
julien@ubuntu:~/0x05$ ./1-swap
a=98, b=42
a=42, b=98



  • Repo
    • GitHub repository: alx-low_level_programming
    • Directory: 0x05-pointers_arrays_strings
    • File: 1-swap.c
    • Example file: 1-main.c

2

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2. This report, by its very length, defends itself against the risk of being read

  • Write a function that returns the length of a string.

    • Prototype: int _strlen(char *s);

  • FYI: The standard library provides a similar function: strlen. Run man strlen to learn more.



  • Repo
    • GitHub repository: alx-low_level_programming
    • Directory: 0x05-pointers_arrays_strings
    • File: 2-strlen.c
    • Example file: 2-main.c

3

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3. I do not fear computers. I fear the lack of them

  • Write a function that prints a string, followed by a new line, to stdout.

    • Prototype: void _puts(char *str);

  • FYI: The standard library provides a similar function: puts. Run man puts to learn more.

julien@ubuntu:~/0x05$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 3-main.c 3-puts.c -o 3-puts
julien@ubuntu:~/0x05$ ./3-puts
I do not fear computers. I fear the lack of them - Isaac Asimov



  • Repo
    • GitHub repository: alx-low_level_programming
    • Directory: 0x05-pointers_arrays_strings
    • File: 3-puts.c
    • Example file: 3-main.c

4

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4. I can only go one way. I've not got a reverse gear

  • Write a function that prints a string, in reverse, followed by a new line.

    • Prototype: void print_rev(char *s);

  • similar function - strrev

julien@ubuntu:~/0x05$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 4-main.c 4-print_rev.c -o 4-print_rev
julien@ubuntu:~/0x05$ ./4-print_rev
vomisA caasI - meht fo kcal eht raef I .sretupmoc raef ton od I



  • Repo
    • GitHub repository: alx-low_level_programming
    • Directory: 0x05-pointers_arrays_strings
    • File: 4-print_rev.c
    • Example file: 4-main.c

5

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5. A good engineer thinks in reverse and asks himself about the stylistic consequences of the components and systems he proposes

  • Write a function that reverses a string.

    • Prototype: void rev_string(char *s);
julien@ubuntu:~/0x05$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 5-main.c 5-rev_string.c -o 5-rev_string
julien@ubuntu:~/0x05$ ./5-rev_string
My School
loohcS yM



  • Repo
    • GitHub repository: alx-low_level_programming
    • Directory: 0x05-pointers_arrays_strings
    • File: 5-rev_string.c
    • Example file: 5-main.c

6

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6. Half the lies they tell about me aren't true

  • Write a function that prints every other character of a string, starting with the first character, followed by a new line.

    • Prototype: void puts2(char *str);
julien@ubuntu:~/0x05$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 6-main.c 6-puts2.c -o 6-puts2
julien@ubuntu:~/0x05$ ./6-puts2
02468



  • Repo
    • GitHub repository: alx-low_level_programming
    • Directory: 0x05-pointers_arrays_strings
    • File: 6-puts2.c
    • Example file: 6-main.c

7

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7. Winning is only half of it. Having fun is the other half

  • Write a function that prints half of a string, followed by a new line.

    • Prototype: void puts_half(char *str);
    • The function should print the second half of the string
    • If the number of characters is odd, the function should print the last n characters of the string, where n = (length_of_the_string - 1) / 2
julien@ubuntu:~/0x05$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 7-main.c 7-puts_half.c -o 7-puts_half
julien@ubuntu:~/0x05$ ./7-puts_half
56789



  • Repo
    • GitHub repository: alx-low_level_programming
    • Directory: 0x05-pointers_arrays_strings
    • File: 7-puts_half.c
    • Example file: 7-main.c

8

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8. Arrays are not pointers

  • Write a function that prints n elements of an array of integers, followed by a new line.

    • Prototype: void print_array(int *a, int n);
    • where n is the number of elements of the array to be printed
    • Numbers must be separated by comma, followed by a space
    • The numbers should be displayed in the same order as they are stored in the array
    • You are allowed to use printf
julien@ubuntu:~/0x05$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 8-main.c 8-print_array.c -o 8-print_array
julien@ubuntu:~/0x05$ ./8-print_array
98, 402, -198, 298, -1024



  • Repo
    • GitHub repository: alx-low_level_programming
    • Directory: 0x05-pointers_arrays_strings
    • File: 8-print_array.c
    • Example file: 8-main.c

9

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9. strcpy

  • Prototype: char *_strcpy(char *dest, char *src);

  • Write a function that copies the string pointed to by src, including the terminating null byte (\0), to the buffer pointed to by dest.

    • Return value: the pointer to dest

  • FYI: The standard library provides a similar function: strcpy. Run man strcpy to learn more.

julien@ubuntu:~/0x05$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 9-main.c 9-strcpy.c -o 9-strcpy
julien@ubuntu:~/0x05$ ./9-strcpy
First, solve the problem. Then, write the code
First, solve the problem. Then, write the code



  • Repo
    • GitHub repository: alx-low_level_programming
    • Directory: 0x05-pointers_arrays_strings
    • File: 9-strcpy.c
    • Example file: 9-main.c

10

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10. Great leaders are willing to sacrifice the numbers to save the people. Poor leaders sacrifice the people to save the numbers

  • Write a function that convert a string to an integer.

    • Prototype: int _atoi(char *s);
    • The number in the string can be preceded by an infinite number of characters
    • You need to take into account all the - and + signs before the number
    • If there are no numbers in the string, the function must return 0
    • You are not allowed to use long
    • You are not allowed to declare new variables of “type” array
    • You are not allowed to hard-code special values
    • We will use the -fsanitize=signed-integer-overflow gcc flag to compile your code.

  • FYI: The standard library provides a similar function: atoi. Run man atoi to learn more.

julien@ubuntu:~/0x05$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 -fsanitize=signed-integer-overflow 100-main.c 100-atoi.c -o 100-atoi
julien@ubuntu:~/0x05$ ./100-atoi
98
-402
-98
214748364
0
402
98
402



  • Repo
    • GitHub repository: alx-low_level_programming
    • Directory: 0x05-pointers_arrays_strings
    • File: 100-atoi.c
    • Example file: 100-main.c

11

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11. Don't hate the hacker, hate the code

  • Create a program that generates random valid passwords for the program 101-crackme.

    • You are allowed to use the standard library
    • You don’t have to pass the betty-style tests (you still need to pass the betty-doc tests)
    • man srand, rand, time
    • gdb and objdump can help
julien@ubuntu:~/0x05$ gcc -Wall -pedantic -Werror -Wextra 101-keygen.c -o 101-keygen
julien@ubuntu:~/0x05$ ./101-crackme "`./101-keygen`"
Tada! Congrats



  • Repo
    • GitHub repository: alx-low_level_programming
    • Directory: 0x05-pointers_arrays_strings
    • File: 101-keygen.c



Dean Robin Otsyeno - [email protected]