Concepts

For this project, we expect you to look at these concepts:

Struggling with the sandbox? Try this: Using Docker & WSL on your local host
Pointers and arrays

Resources

Read or watch:

C - Pointer to Pointer
C – Pointer to Pointer with example
Multi-dimensional Arrays in C
Two dimensional (2D) arrays in C programming with example

Additional Resources

Arrays, Strings & Pointers in C Programming

Learning Objectives

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

General

What are pointers to pointers and how to use them
What are multidimensional arrays and how to use them
What are the most common C standard library functions to manipulate strings

Requirements

General

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

More Info

You do not need to learn about pointers to functions, arrays of structures, malloc and free - yet.

Quiz questions

Question #0

What is the size of *p in this code?

int *p;

4 bytes
8 bytes
16 bytes

Question #1

What is stored inside a pointer to a pointer to an int?

An address where an int is stored
An int
An address where an address is stored

Question #2

What is the size of p in this code?

int *p;

4 bytes
8 bytes
16 bytes

Question #3

In this following code, what is the value of a[3][0]?

int a[5][2] = {{1, 2}, {3, 4}, {5, 6}, {7, 8}, {9, 10}};

5
7
8
{7, 8}

Question #4

What is the size of p in this code?

int **p;

4 bytes
8 bytes
16 bytes

Question #5

In this following code, what is the value of a[0][0]?

int a[5][2] = {{1, 2}, {3, 4}, {5, 6}, {7, 8}, {9, 10}};

4
1
2
3

Question #6

In this following code, what is the value of a[3][1]?

int a[5][2] = {{1, 2}, {3, 4}, {5, 6}, {7, 8}, {9, 10}};

8
7
9
{7, 8}

Question #7

What is the size of *p in this code?

int **p;

4 bytes
8 bytes
16 bytes

Question #8

In this following code, what is the value of a[1][1]?

int a[5][2] = {{1, 2}, {3, 4}, {5, 6}, {7, 8}, {9, 10}};

4
1
2
3

Tasks

0. memset

Write a function that fills memory with a constant byte.

Prototype: char *_memset(char *s, char b, unsigned int n);
The _memset() function fills the first n bytes of the memory area pointed to by s with the constant byte b
Returns a pointer to the memory area s

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

julien@ubuntu:~/0x07$ cat 0-main.c
#include "main.h"
#include <stdio.h>

/**
 * simple_print_buffer - prints buffer in hexa
 * @buffer: the address of memory to print
 * @size: the size of the memory to print
 *
 * Return: Nothing.
 */
void simple_print_buffer(char *buffer, unsigned int size)
{
        unsigned int i;

        i = 0;
        while (i < size)
        {
                if (i % 10)
                {
                        printf(" ");
                }
                if (!(i % 10) && i)
                {
                        printf("\n");
                }
                printf("0x%02x", buffer[i]);
                i++;
        }
        printf("\n");
}

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    char buffer[98] = {0x00};

    simple_print_buffer(buffer, 98);
    _memset(buffer, 0x01, 95);
    printf("-------------------------------------------------\n");
    simple_print_buffer(buffer, 98);
    return (0);
}
julien@ubuntu:~/0x07$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 0-main.c 0-memset.c -o 0-memset
julien@ubuntu:~/0x07$ ./0-memset
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
-------------------------------------------------
0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01
0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01
0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01
0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01
0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01
0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01
0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01
0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01
0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01 0x01
0x01 0x01 0x01 0x01 0x01 0x00 0x00 0x00
julien@ubuntu:~/0x07$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x07-pointers_arrays_strings
File: 0-memset.c

1. memcpy

Write a function that copies memory area.

Prototype: char *_memcpy(char *dest, char *src, unsigned int n);
The _memcpy() function copies n bytes from memory area src to memory area dest
Returns a pointer to dest

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

julien@ubuntu:~/0x07$ cat 1-main.c
#include "main.h"
#include <stdio.h>

/**
 * simple_print_buffer - prints buffer in hexa
 * @buffer: the address of memory to print
 * @size: the size of the memory to print
 *
 * Return: Nothing.
 */
void simple_print_buffer(char *buffer, unsigned int size)
{
    unsigned int i;

    i = 0;
    while (i < size)
    {
        if (i % 10)
        {
            printf(" ");
        }
        if (!(i % 10) && i)
        {
            printf("\n");
        }
        printf("0x%02x", buffer[i]);
        i++;
    }
    printf("\n");
}

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    char buffer[98] = {0};
    char buffer2[98] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14};

    simple_print_buffer(buffer, 98);
    _memcpy(buffer + 50, buffer2, 10);
    printf("-------------------------------------------------\n");
    simple_print_buffer(buffer, 98);
    return (0);
}
julien@ubuntu:~/0x07$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 1-main.c 1-memcpy.c -o 1-memcpy
julien@ubuntu:~/0x07$ ./1-memcpy
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
-------------------------------------------------
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x01 0x02 0x03 0x04 0x05 0x07 0x07 0x08 0x09 0x0a
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
julien@ubuntu:~/0x07$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x07-pointers_arrays_strings
File: 1-memcpy.c

2. strchr

Write a function that locates a character in a string.

Prototype: char *_strchr(char *s, char c);
Returns a pointer to the first occurrence of the character c in the string s, or NULL if the character is not found

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

julien@ubuntu:~/0x07$ cat 2-main.c
#include "main.h"
#include <stdio.h>

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    char *s = "hello";
    char *f;

    f = _strchr(s, 'l');

    if (f != NULL)
    {
        printf("%s\n", f);
    }
    return (0);
}
julien@ubuntu:~/0x07$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 2-main.c 2-strchr.c -o 2-strchr
julien@ubuntu:~/0x07$ ./2-strchr
llo
julien@ubuntu:~/0x07$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x07-pointers_arrays_strings
File: 2-strchr.c

3. strspn

Write a function that gets the length of a prefix substring.

Prototype: unsigned int _strspn(char *s, char *accept);
Returns the number of bytes in the initial segment of s which consist only of bytes from accept

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

julien@ubuntu:~/0x07$ cat 3-main.c
#include "main.h"
#include <stdio.h>

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    char *s = "hello, world";
    char *f = "oleh";
    unsigned int n;

    n = _strspn(s, f);
    printf("%u\n", n);
    return (0);
}
julien@ubuntu:~/0x07$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 3-main.c 3-strspn.c -o 3-strspn
julien@ubuntu:~/0x07$ ./3-strspn
5
julien@ubuntu:~/0x07$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x07-pointers_arrays_strings
File: 3-strspn.c

4. strpbrk

Write a function that searches a string for any of a set of bytes.

Prototype: char *_strpbrk(char *s, char *accept);
The _strpbrk() function locates the first occurrence in the string s of any of the bytes in the string accept
Returns a pointer to the byte in s that matches one of the bytes in accept, or NULL if no such byte is found

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

julien@ubuntu:~/0x07$ cat 4-main.c
#include "main.h"
#include <stdio.h>

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    char *s = "hello, world";
    char *f = "world";
    char *t;

    t = _strpbrk(s, f);
    printf("%s\n", t);
    return (0);
}
julien@ubuntu:~/0x07$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 4-main.c 4-strpbrk.c -o 4-strpbrk
julien@ubuntu:~/0x07$ ./4-strpbrk
llo, world
julien@ubuntu:~/0x07$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x07-pointers_arrays_strings
File: 4-strpbrk.c

5. strstr

Write a function that locates a substring.

Prototype: char *_strstr(char *haystack, char *needle);
The _strstr() function finds the first occurrence of the substring needle in the string haystack. The terminating null bytes (\0) are not compared
Returns a pointer to the beginning of the located substring, or NULL if the substring is not found.

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

julien@ubuntu:~/0x07$ cat 5-main.c
#include "main.h"
#include <stdio.h>

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    char *s = "hello, world";
    char *f = "world";
    char *t;

    t = _strstr(s, f);
    printf("%s\n", t);
    return (0);
}
julien@ubuntu:~/0x07$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 5-main.c 5-strstr.c -o 5-strstr
julien@ubuntu:~/0x07$ ./5-strstr
world
julien@ubuntu:~/0x07$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x07-pointers_arrays_strings
File: 5-strstr.c

6. Chess is mental torture

Write a function that prints the chessboard.

Prototype: void print_chessboard(char (*a)[8]);

julien@ubuntu:~/0x07$ cat 7-main.c
#include "main.h"
#include <stdio.h>

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    char board[8][8] = {
        {'r', 'k', 'b', 'q', 'k', 'b', 'k', 'r'},
        {'p', 'p', 'p', 'p', 'p', 'p', 'p', 'p'},
        {' ', ' ', ' ', ' ', ' ', ' ', ' ', ' '},
        {' ', ' ', ' ', ' ', ' ', ' ', ' ', ' '},
        {' ', ' ', ' ', ' ', ' ', ' ', ' ', ' '},
        {' ', ' ', ' ', ' ', ' ', ' ', ' ', ' '},
        {'P', 'P', 'P', 'P', 'P', 'P', 'P', 'P'},
        {'R', 'K', 'B', 'Q', 'K', 'B', 'K', 'R'},
    };
    print_chessboard(board);
    return (0);
}
julien@ubuntu:~/0x07$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 _putchar.c 7-main.c 7-print_chessboard.c -o 7-print_chessboard
julien@ubuntu:~/0x07$ ./7-print_chessboard
rkbqkbkr
pppppppp




PPPPPPPP
RKBQKBKR
julien@ubuntu:~/0x07$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x07-pointers_arrays_strings
File: 7-print_chessboard.c

7. The line of life is a ragged diagonal between duty and desire

Write a function that prints the sum of the two diagonals of a square matrix of integers.

Prototype: void print_diagsums(int *a, int size);
Format: see example
You are allowed to use the standard library

Note that in the following example we are casting an int[][] into an int*. This is not something you should do. The goal here is to make sure you understand how an array of array is stored in memory.

julien@ubuntu:~/0x07$ cat 8-main.c
#include "main.h"
#include <stdio.h>

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    int c3[3][3] = {
        {0, 1, 5},
        {10, 11, 12},
        {1000, 101, 102},
    };
    int c5[5][5] = {
        {0, 1, 5, 12124, 1234},
        {10, 11, 12, 123521, 12512},
        {1000, 101, 102, 12545, 214543435},
        {100, 1012451, 11102, 12545, 214543435},
        {10, 12401, 10452, 11542545, 1214543435},
    };
    print_diagsums((int *)c3, 3);
    print_diagsums((int *)c5, 5);
    return (0);
}
julien@ubuntu:~/0x07$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 8-main.c 8-print_diagsums.c -o 8-print_diagsums
julien@ubuntu:~/0x07$ ./8-print_diagsums
113, 1016
1214556093, 1137318
julien@ubuntu:~/0x07$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x07-pointers_arrays_strings
File: 8-print_diagsums.c

8. Double pointer, double fun

Write a function that sets the value of a pointer to a char.

Prototype: void set_string(char **s, char *to);

julien@ubuntu:~/0x07$ cat 100-main.c
#include "main.h"
#include <stdio.h>

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    char *s0 = "Bob Dylan";
    char *s1 = "Robert Allen";

    printf("%s, %s\n", s0, s1);
    set_string(&s1, s0);
    printf("%s, %s\n", s0, s1);
    return (0);
}
julien@ubuntu:~/0x07$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 100-main.c 100-set_string.c -o 100-set_string
julien@ubuntu:~/0x07$ ./100-set_string
Bob Dylan, Robert Allen
Bob Dylan, Bob Dylan
julien@ubuntu:~/0x07$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x07-pointers_arrays_strings
File: 100-set_string.c

9. My primary goal of hacking was the intellectual curiosity, the seduction of adventure

Create a file that contains the password for the crackme2 executable.

Your file should contain the exact password, no new line, no extra space
ltrace, ldd, gdb and objdump can help
You may need to install the openssl library to run the crakme2 program: sudo apt install libssl-dev
Edit the source list sudo nano /etc/apt/sources.list to add the following line: deb http://security.ubuntu.com/ubuntu xenial-security main Then sudo apt update and sudo apt install libssl1.0.0

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x07-pointers_arrays_strings
File: 101-crackme_password

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README.md

README.md

Concepts

Resources

Additional Resources

Learning Objectives

General

Requirements

General

More Info

Quiz questions

Question #0

Question #1

Question #2

Question #3

Question #4

Question #5

Question #6

Question #7

Question #8

Tasks

0. memset

1. memcpy

2. strchr

3. strspn

4. strpbrk

5. strstr

6. Chess is mental torture

7. The line of life is a ragged diagonal between duty and desire

8. Double pointer, double fun

9. My primary goal of hacking was the intellectual curiosity, the seduction of adventure

Files

README.md

Latest commit

History

README.md

File metadata and controls

Concepts

Resources

Additional Resources

Learning Objectives

General

Requirements

General

More Info

Quiz questions

Question #0

Question #1

Question #2

Question #3

Question #4

Question #5

Question #6

Question #7

Question #8

Tasks

0. memset

1. memcpy

2. strchr

3. strspn

4. strpbrk

5. strstr

6. Chess is mental torture

7. The line of life is a ragged diagonal between duty and desire

8. Double pointer, double fun

9. My primary goal of hacking was the intellectual curiosity, the seduction of adventure