0x05. C - Pointers, arrays and strings

By Julien Barbier

Concepts

For this project, students are expected to look at these concepts:

Pointers and arrays
Data Structures

Resources

Read or watch:

C - Arrays
C - Pointers
C - Strings
Memory Layout

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 and how to use them
What are arrays and how to use them
What are the differences between pointers and arrays
How to use strings and how to manipulate them
Scope of variables

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

Tasks

0. 98 Battery st.

mandatory

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$ cat 0-main.c
#include "main.h"
#include <stdio.h>

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    int n;

    n = 402;
    printf("n=%d\n", n);
    reset_to_98(&n);
    printf("n=%d\n", n);
    return (0);
}
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
julien@ubuntu:~/0x05$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x05-pointers_arrays_strings
File: 0-reset_to_98.c

Done? Help Check your code

1. Don't swap horses in crossing a stream

mandatory

Write a function that swaps the values of two integers.

Prototype: void swap_int(int *a, int *b);

julien@ubuntu:~/0x05$ cat 1-main.c
#include "main.h"
#include <stdio.h>

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    int a;
    int b;

    a = 98;
    b = 42;
    printf("a=%d, b=%d\n", a, b);
    swap_int(&a, &b);
    printf("a=%d, b=%d\n", a, b);
    return (0);
}
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
julien@ubuntu:~/0x05$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x05-pointers_arrays_strings
File: 1-swap.c

Done? Help Check your code

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

mandatory

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.

julien@ubuntu:~/0x05$ cat 2-main.c
#include "main.h"
#include <stdio.h>

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    char *str;
    int len;

    str = "My first strlen!";
    len = _strlen(str);
    printf("%d\n", len);
    return (0);
}
julien@ubuntu:~/0x05$ gcc -Wall -pedantic -Werror -Wextra -std=gnu89 2-main.c 2-strlen.c -o 2-strlen
julien@ubuntu:~/0x05$ ./2-strlen
16
julien@ubuntu:~/0x05$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x05-pointers_arrays_strings
File: 2-strlen.c

Done? Help Check your code

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

mandatory

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$ cat 3-main.c
#include "main.h"

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    char *str;

    str = "I do not fear computers. I fear the lack of them - Isaac Asimov";
    _puts(str);
    return (0);
}
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
julien@ubuntu:~/0x05$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x05-pointers_arrays_strings
File: 3-puts.c

Done? Help Check your code

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

mandatory

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

Prototype: void print_rev(char *s);

julien@ubuntu:~/0x05$ cat 4-main.c
#include "main.h"

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    char *str;

    str = "I do not fear computers. I fear the lack of them - Isaac Asimov";
    print_rev(str);
    return (0);
}
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
julien@ubuntu:~/0x05$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x05-pointers_arrays_strings
File: 4-print_rev.c

Done? Help Check your code

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

mandatory

Write a function that reverses a string.

Prototype: void rev_string(char *s);

julien@ubuntu:~/0x05$ cat 5-main.c
#include "main.h"
#include <stdio.h>

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    char s[10] = "My School";

    printf("%s\n", s);
    rev_string(s);
    printf("%s\n", s);
    return (0);
}
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
julien@ubuntu:~/0x05$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x05-pointers_arrays_strings
File: 5-rev_string.c

Done? Help Check your code

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

mandatory

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$ cat 6-main.c
#include "main.h"

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    char *str;

    str = "0123456789";
    puts2(str);
    return (0);
}
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
julien@ubuntu:~/0x05$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x05-pointers_arrays_strings
File: 6-puts2.c

Done? Help Check your code

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

mandatory

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$ cat 7-main.c
#include "main.h"

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    char *str;

    str = "0123456789";
    puts_half(str);
    return (0);
}
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
julien@ubuntu:~/0x05$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x05-pointers_arrays_strings
File: 7-puts_half.c

Done? Help Check your code

8. Arrays are not pointers

mandatory

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$ cat 8-main.c
#include "main.h"

/**
 * main - check the code for
 *
 * Return: Always 0.
 */
int main(void)
{
    int array[5];

    array[0] = 98;
    array[1] = 402;
    array[2] = -198;
    array[3] = 298;
    array[4] = -1024;
    print_array(array, 5);
    return (0);
}
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
julien@ubuntu:~/0x05$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x05-pointers_arrays_strings
File: 8-print_array.c

Done? Help Check your code

9. strcpy

mandatory

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$ cat 9-main.c
#include "main.h"
#include <stdio.h>

/**
 * main - check the code
 *
 * Return: Always 0.
 */
int main(void)
{
    char s1[98];
    char *ptr;

    ptr = _strcpy(s1, "First, solve the problem. Then, write the code\n");
    printf("%s", s1);
    printf("%s", ptr);
    return (0);
}
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
julien@ubuntu:~/0x05$

Repo:

GitHub repository: alx-low_level_programming
Directory: 0x05-pointers_arrays_strings
File: 9-strcpy.c

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README.md

README.md

0x05. C - Pointers, arrays and strings

Concepts

Resources

Learning Objectives

General

Requirements

General

Tasks

0. 98 Battery st.

1. Don't swap horses in crossing a stream

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

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

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

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

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

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

8. Arrays are not pointers

9. strcpy

Files

README.md

Latest commit

History

README.md

File metadata and controls

0x05. C - Pointers, arrays and strings

Concepts

Resources

Learning Objectives

General

Requirements

General

Tasks

0. 98 Battery st.

1. Don't swap horses in crossing a stream

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

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

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

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

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

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

8. Arrays are not pointers

9. strcpy